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Asus Zenfone 2 ZE551ML Review

This is our 3rd Zenfone 2 review this month and this time, we have the high-end variant of the handset — the ZE551ML which sports a full HD display, quad-core 1.8GHz processor and 4GB of RAM. In this article, we will tackle the Zenfone 2 ZE551ML and complete the whole review series.

The ZE551ML is the high-end variant of the Zenfone 2 family. There’s the ZE500CL which is a 5-incher and then the ZE550ML which sports up to 2GB of RAM and a 1.8GHz quad-core processor with 720p display.

We already have a separate full review of the ZE500CL and the ZE550ML but for the purpose of this article, we’re basing our results on the ZE551ML variant that comes with full HD display, quad-core 1.8GHz processor and 4GB of RAM.

By the time of this review, we also received a firmware update (110MB) that address some bugs and fixed stability issues (including the camera app crashing when taking HDR photos).

Design and Construction

Asus continued to use their signature design and form factor from the original Zenfone 4, 5 and 6 then improved a little bit to incorporate in the Zenfone 2. Hence, it’s pretty easy to confuse the Zenfone 2 from the Zenfone 5 or Zenfone 6 if you’re not very familiar with the family. The most obvious distinction for the Zenfone 2 would be the rear volume keys and the brushed metal finish at the back.

With a 5.5-inch display, the ZE551ML looks huge but still feels comfortable in the hands. It’s bigger than the G3 even though they have the same display size. The bezels are also quite thick at 3.3mm, despite Asus’ claims that it’s already narrow.

Based on our side-by-side observation, the bezels are as thick (or slightly thicker) than the side bezels of the HTC One M8 and close to 3 times as thick as the 1.15mm bezel of the LG G3. The Android capacitive buttons are still there at the bottom end (Back, Home, Recent Apps) which should have been already replaced by one-screen buttons due to Kitkat/Lollipop UI implementation.

Build quality is really good, feels solid on the hands with a comfortable grip thanks to that curved back; not too heavy or bulky either. The back cover is removable to expose access to the two micro-SIM card slots and a microSD card slot. The first SIM card slot supports up to 4G networks while the second SIM card slot only supports 2G networks.

The battery is visible but cannot be readily removed due to the card slots blocking the battery. The only way to remove is by loosening the screws around the back.

The power button is found at the top together with the 3.5mm audio port. The volume keys are at the back, just below the rear camera and dual-LED flash. The back cover has a brushed metal finish giving it a nice texture that’s closely similar to that of the LG G3. Of the various colors, we liked the red one the most.

With it’s rather large size, it’s quite hard to use the Zenfone 2 with one hand so you’ll always end up texting using both hands. The placement of the rear key was inspired from the LG G2 and LG G3 and works as well especially when the device is this large. What’s a little odd is the placement of the power button at the top.

Display and Multimedia

The 5.5-inch IPS LCD display looks pretty good and surprisingly crisp and clear at full HD resolution. Colors are vibrant well saturated.

There’s still some degree of outdoor visibility but the screen is also very reflective especially under direct sunlight. When indoors, cranking up the brightness at the lowest level is still comfortable and ideal brightness level would be around 70%. This means the display is still very usable even at lower brightness settings allowing you to conserve more battery life.

The display is also protected by a very tough Corning Gorilla Glass 3 in order to avoid the usual hairline scratches on the glass panel. Nevertheless, we think a lot of new owners would still put an additional tempered glass or protective film once they open their units out of the box.

The large screen is just about right when surfing the web, watching movies or playing games for a couple of hours. The screen color mode allows you to change the color temperature of the display to your liking. There are also color presets like Balance, Reading, Vivid and a custom one you can save.

Asus claims a screen-to-body ratio of 72% which is right around the alley of the OnePlus One (71.9%), Lenovo Vibe Z ( 72.7%), OPPO Find 7 (72.9%) while the LG G3 is at 76.3%.

The loudspeakers at the back sounded good, has decent volume range but did not have bass in it. The four rows of pinholes for the loudspeaker is just for symmetry since opening the back cover will reveal the speakers to be smaller and flushed to the left side. The earphones that came with it are good too but nothing really spectacular about them.

OS, UI, and Apps

Asus did a pretty good job having Android 5.0 Lollipop with the Zenfone 2 right out of the box. Our review unit also had about 130MB worth of firmware updates downloaded via OTA right after we booted it up for the first time.

The Asus ZenUI looks simple yet really clean and nice with very little footprint so it feels light and almost bloatware-free. The pre-installed Zenlink collection includes PC Link, Remote Link, Share Link and Party Link. Of the 32GB internal storage, about 25.5GB is usable so we think it’s more than enough for the meantime.

There are a few customizations and refinements introduced with the ZenUI. While you’re limited to a maximum of 7 home screens, you can customize the scroll effects, transitions and animations to your liking.

Even the Folders can be customized to various arrangements (2×2 grid, 3×3 grid, stack, fan, line or card). You can likewise download additional sets of icon packs if you don’t want the flat look of the default one. There are not a lot of native widgets though.

There’s an Easy Mode you can switch to in order to make the whole UI more simplified and accessible. The Zen Motion allows for gesture actions like “shake to screenshot” and “double tap to wake and sleep”.

There’s even that gesture motion on the screen where you can draw a specific letter to wake up the screen and immediately run an app or feature. The first time we saw that was with the Oppo Color OS. It’s quite apparent that Asus learned a trick or two from other vendors and incorporated them to the Zen UI.


Asus has been boasting its PixelMaster camera since the first Zenfone and the Zenfone 2 claims to have better optics, starting with the 13-megapixel rear camera.

We took notice that even the sensor on the Zenfone 5 can get good exposure even on low-light environments. That holds true with the Zenfone 2.

[fancygallery id=”196″ album=”238″]

Samples above show the 13MP rear camera of the Zenfone 2 takes really good photos in general with much better results in macro mode. Low-light photos appear brighter than usual, thanks to PixelMaster, but accuracy on focus is a hit or miss (we took 4 successive shots of the grill picture above and only 2 out of 4 in focus).

Video recording is equally good at full HD 1080p. There is video stabilization but that is limited to 720p resolution.

There are a lot of options to tinker around with the camera alone — from setting manual ISO between 50 to 800, exposure values form -2 to 2, anti-flicker from 50Hz to 60Hz, anti-shake enhancements and HDR.

Performance and Benchmarks

Running an Intel Atom Z3560 quad-core processor paired with a generous 4GB of RAM works really well with Android 5.0 Lollipop. Navigation and transitions is smooth and snappy. Apps and games run just fine and multitab browsing on Chrome is effortless.

The Z3560 is a slightly newer Atom processor, launched in 2nd quarter of 2014. It has 4 cores, 4 threads and supports 64-bit operations and up to 4GB of RAM. Each core operates from 500MHz to 1.83GHz, depending on the load required. The other processor variant is the Z3580 2.3GHz (we’ll do a separate benchmark and battery test here).

Here are the test results of the benchmarks we ran on the unit:

Asus Zenfone 2 ZE550MLAsus Zenfone 2 ZE500CLAsus Zenfone 2 ZE551ML
Quadrant Standard18,9798,18218,565
Antutu Benchmark41,96823,23139,537
Vellamo2,985 (Chrome)1366 (Chrome)2,991 (Chrome)
1,194 (Metal)646 (Metal)1,108 (Metal)
1,357 (Multicore)938 (Multicore)1,331 (Multicore)
PCMark 5,018 (Android Work)3,573 (Android Work)5,092 (Android Work)

Take note that the ZE551ML used here runs on the same 1.8GHz processor as the ZE550ML, thus the benchmark scores are either the same or lower due to the higher display resolution.

Update: You can check the benchmark scores of the 2.3GHz version here.

ZE550ML 2GB/1.8GHzZE551ML 4GB/1.8GHzZE551ML 4GB/2.3GHz
3DMark15,816 (Ice Storm Unlimited)18,814 (Ice Storm Unlimited)20,026 (Ice Storm Unlimited)
PCMark 5,018 (Android Work)5,092 (Android Work)5,597 (Android Work)
Vellamo2,985 (Chrome)
1,194 (Metal)
1,357 (Multicore)
2,991 (Chrome)
1,108 (Metal)
1,331 (Multicore)
3,374 (Chrome)
1,240 (Metal)
1,424 (Multicore)

After running a number of resource-intensive applications, the device gets a bit warm but nothing alarming of sorts. So far, even running 3DMark Ice Storm Unlimited and Epic Citadel only caused slight warming of the middle section of the back side. For the 2.3GHz version however, we recorded a maximum core temperature of 50.2 Celsius.

Compared to the benchmark results of the ZE550ML, the ZE551ML 1.8GHz actually got lower scores on graphics-related benchmarks like PCMark and 3DMark. This is mainly due to the full HD 1080p display of the latter.

Connectivity and Call Quality

One of the highlights if the new Zenfone 2 is the dual-SIM capability with LTE support. While only the first micro-SIM slot supports connectivity up to 4G, the second micro-SIM slot can only handle up to 2G.

LTE connectivity is pretty string with multiple speed tests on different locations yielding 13Mbps downlink speeds (using Smart LTE postpaid SIM). Calls are clear and crisp on both SIM cards while SMS handling for the dual-SIM functionality is very easy to get used to.

Unlike the lower variants of the Zenfone 2, the ZE551ML has a built-in NFC radio.

Battery Life

The Zenfone 5 has been heavily criticized before for having very poor battery life. This is mainly due to the architecture of the Intel Atom processor. So, it’s no surprise that a lot of people will still be skeptic with the Zenfone 2 despite its generous 3,000mAh Li-Po battery.

As for battery life nominal tests, we managed around 8 hours on a full charge using our standard battery bench at 50% brightness and 0% volume playing an HD movie.

We also got 7:07 hours when we tested it with PCMark Battery Test at 50% brightness in Flight Mode. 2.3GHz version did almost the same at 6:56 hours.

That’s almost exactly the same results we got from the HTC One M8 (7:08 hours) with its 2,600mAh battery. Only shows Snapdragon chips are still better than Intel Atom in terms of battery efficiency.

The results are a little bit below the average range of other smartphones we’ve tested before but is still way better than the performance of the Zenfone 5. The ZE551ML is shorter by 1 hour compared to the ZE550ML (8:06 hours). Despite the 4GB of RAM, the full HD resolution shaved off about 12% of the battery life from a 720p equivalent.

The 2.3GHz version of the ZE551ML also supports fast charging (BoostMaster). The adaptor that came in the box can pump as much as 2A @ 5V and 9V of juice which results to a charging time of just 2.5 to 2.75 hours to 100%.

The 1.8GHz version does not support BoostMaster which allows for very fast charging time.


It’s no secret Asus has generated a lot of interest in the Zenfone 2, fueled by their earlier success with the Zenfone 5 last year. The Zenfone 2 ZE551ML promises a significant upgrade to the Zenfone line-up.

It comes with a familiar and solid design, pretty good hardware with LTE support, all packed in a very price-conscious offering. We’re pretty sure Asus will be selling hundreds of thousands of these units once they become officially available in the Philippines this May.

Asus has once again proven that you can get a really good, solid smartphone at a very reasonable price without any compromise. The Zenfone 2 is a testament to that.

ASUS Zenfone 2 (ZE551ML) specs:
5.5-inch full HD IPS display, 1920×1080 pixels @ 403ppi
Corning Gorilla Glass 3
Intel Atom Z3560 1.8GHz 64-bit quad-core processor
PowerVR G6430 GPU
32GB internal storage
up to 64GB via microSD
13 megapixel Pixel Master camera w/ dual LED flash
5 megapixel front camera
Dual-SIM, Dual Active
WiFi 802.11 a/b/g/n
Bluetooth 4.0, A2DP, EDR
GPS with aGPS support, GLONASS
Android 5.0 Lollipop w/ ZenUI
Li-Ion 3,000mAh battery
152.5 x 77.2 x 10.9mm (dimensions)
170 grams (weight)

What we liked about it:
* Very affordable
* Great performance
* Good camera
* LTE support
* NFC support
* Android Lollipop out of the box
* Nice, simple ZenUI

What we did not like:
* A little bit on the heavy and chunky side
* Below average battery life
* Non-removable battery

Related Reviews:

Author’s Note: This review unit was bought from Widget City (see listing here).

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Avatar for Abe Olandres

Abe is the founder and Editor-in-Chief of YugaTech with over 20 years of experience in the technology industry. He is one of the pioneers of blogging in the country and considered by many as the Father of Tech Blogging in the Philippines. He is also a technology consultant, a tech columnist with several national publications, resource speaker and mentor/advisor to several start-up companies.

52 Responses

  1. Avatar for Jonathan Pensotes Jonathan Pensotes says:

    My 1Month old (from date of purchase) ASUS_Z00AD (ZE551ML) died after an ASUS System/Firmware update early this morning. The phone seems to have halted its charging capability since neither the screen nor the led indicator shows otherwise. While connected to a charging port, it’s built-in battery shows signs of overheating so i opted from trying it out again. It’s repair/revival/replacement is up to E World Celphone & Accessories at Allen Avenue, Catbalogan City, Samar and ASUS Philippines now. Purchase was made on the 4th of December 2015 and the unit have had several ASUS System and Firmware Updates since then, up until last night. E World already has possession of the unit but the warranty cards, and the unit’s box and other accessories are still with me, they said that it will take 1-2 Months processing whether parts of the phone will be replaced or not and whether I will be charged for either the revival/repair/replacement (which seems to be unfair to my part but hey i’m giving them a chance). I have also sent a technical complaint to ASUS Philippines regarding the product’s malfunction due to a software/firmware update and awaits their response. Meanwhile, I’ll be keenly observing how my consumer welfare and protection rights are either exploited or upheld. It’s a beautiful piece of technology and I am in mourning for its untimely demise. Prayers for a positive resolution to this inconvenience are welcomed.lol

    • Avatar for maynard escobar maynard escobar says:

      meron po ba sa sm marikina or cubao nito at anu po ung price nya thanks

  2. how to know if your asus ze551ml has a 2.3 GHZ or a 1.8 GHZ pls answer .. interested buyer here .. :)

  3. Avatar for Marc Marc says:

    If i were a gadget i want to be ASUS Zenphone :)

  4. Avatar for Bizzaviet Bizzaviet says:

    Where I can buy it in Viet Nam? Please tell me, I want to buy it

    • Avatar for jason jason says:

      u can buy it by lifting a rock, then throw it in the sky 180 degrees above you. wait for it to come down then it will be there.

      moron, go to the phone shop !

  5. Avatar for haha haha says:

    sim 2 doesn’t support data which is the biggest disaapointment for this phone. dual data support for dual sim phone is very basic, even cherry mobile which one third of the price has that feature.

  6. Avatar for Kits Amores Kits Amores says:

    Sobrang love ko tong phone na to. Sobrang smooth ng performance and ganda ng camera! Walang lag. Walang hassle. Design and performance all in one phone! Great review yugatech! =)

  7. Avatar for niwra niwra says:

    Meron po ba kayong issues bout sd card? Hindi po kc nareread ung king com 16gb class 10 ko..anu po ba dapat gawin or gmiting mmc..zenfone2 2gb ram user here..tnx for the reply..

  8. Avatar for Joker Arroyo Joker Arroyo says:

    Magana pdin ang Cloudfone thrill 530qx kasi napakatagal ng attery nya kung I op lang yung battey capacity ng asus zenfone 2 ok na ok na to. . .

  9. Avatar for meit_nerium meit_nerium says:

    YUGATECH which woukd be a better buy, microsoft lumia 640 xl or asus zenfone 2? Camera is my top priority po.

  10. Avatar for kurnoy kurnoy says:

    Disappointed ako sa Sim 2 kasi 2G network lang. If pupunta ka to another country for example Korea syempre like mo dalhin dual sim phone. Pero pagdating mo dun useless ang dual sim mo kasi wala na silang 2G. obsolete na network and was phased out technology. 3G na minimum nila dun..Kaya mas maganda ang Starmobile Knight X for me. First announcement ng specs ng zenfone 2 e dual LTE switching, yun pala hindi,, sayang pera ko huhuhu

  11. Avatar for Lawfer Lawfer says:

    Hi Yuga, need some advice please. If you could buy Asus Zenfone 2 (4GB RAM version, with 32GB ata) and LG G3 (16GB only) at the same price, which one would you choose? Anong pros and cons para sa inyo? Thanks in advance sa magko-comment.

    • Avatar for Abe Olandres Abe Olandres says:

      Biggest different is the price. G3 has better performance, battery life and camera. Z2 has larger storage, ram and lower price.

    • Avatar for Lawfer Lawfer says:

      Thanks for the reply. I posted the questions since I might be able to get either one at the same price because of ongoing promotions where I am based. Not entirely sure, maybe the G3 would be a bit more expensive, but only by a few hundred pesos. Plus the G3 I can buy now, the ZF2 I have to wait for by the end of the month. Thanks again! :)

    • Avatar for Abe Olandres Abe Olandres says:

      G3 it is. :)

  12. Avatar for heh heh says:

    How to update firmware? There’s no system update in settings>about

  13. Avatar for toybits toybits says:

    “The 1.8GHz version does not support BoostMaster which allows for very fast charging time”

    as posted above, but seems not true. BoostMaster was confirmed working on Asus ZF2 550ML at XDA forum

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