Product Listing

ASUS ZenFone 2 ZE551ML (4GB RAM) - Great value from Singapore's first 4GB RAM smartphone

By PY Ho & James Lu - 28 Apr 2015
Launch SRP: S$429

Overview, Design & Features


In 2014, ASUS launched the ZenFone series, a new range of Intel Atom-powered smartphones with value-based offerings, designed to compete against the likes of Xiaomi and Oppo. Last year, we saw the ZenFone 4, ZenFone 5, and ZenFone 6, and now ASUS has launched the ZenFone 2. Wait, what? If ASUS's naming conventions seem confusing (and they are), allow us to explain. 

The original ZenFone came in three screen sizes: 4-inch, 5-inch, and 6-inch (thus, 4, 5, 6). This year's ZenFone ditches the screen size naming and is so called simply because it's the second-generation ZenFone. What happens two years from now when ASUS gets onto the 4th generation ZenFone?

Even more confusingly, despite ditching the screen-size model names, this year's ZenFone is also available in different screen sizes: 5-inch and 5.5-inch. And the 5.5-inch model is available in both Full HD or 720p options.

But that's not all.

The 5.5-inch Full HD ZenFone 2 itself comes in two configurations, one with 2GB RAM and one with 4GB RAM and a speedier processor. And the 4GB RAM version also comes in two storage capacities, 32GB and 64GB (exclusive to Singtel).

Confused yet? Here's a table showing all of the ZenFone 2 variations:

ASUS ZenFone 2 Variants
  ASUS ZenFone 2 ZE551ML (4GB RAM) ASUS ZenFone 2 ZE551ML (2GB RAM) ASUS ZenFone 2 ZE550ML ASUS ZenFone 2 ZE500CL
  ASUS ZenFone 2 ZE551ML (4GB RAM) ASUS ZenFone 2 ZE551ML (2GB RAM) ASUS ZenFone 2 ZE550ML ASUS ZenFone 2 ZE500CL
Launch SRP
  • From S$429
  • From S$349
  • From S$299
  • From S$249
Operating system
  • Android 5.0 Lollipop with ZenUI
  • Android 5.0 Lollipop with ZenUI
  • Android 5.0 Lollipop with ZenUI
  • Android 5.0 Lollipop with ZenUI
  • Intel Atom Z3580 quad-core 2.3 GHz
  • Intel Atom Z3560 quad-core 1.8 GHz
  • Intel Atom Z3560 Quad-core 1.8 GHz
  • Intel Atom Z2560 dual-core 1.6 GHz
Built-in Memory
  • 4GB RAM
  • 2GB RAM
  • 2GB RAM
  • 2GB RAM
  • 5.5-inch / 1920 x 1080 pixels (403ppi) / IPS
  • 5.5-inch / 1,920 x 1,080 pixels (403ppi) / IPS
  • 5.5-inch / 1280 x 720 pixels (267ppi) / IPS
  • 5-inch / 1280 x 720 pixels (294 ppi) / IPS
  • Rear: 13-megapixel, f/2.0, 5-element lens and PixelMaster technology
  • Front: 5-megapixel, f/2.0
  • Rear: 13-megapixel, f2.0, 5-element lens and PixelMaster technology
  • Front: 5-megapixel, f/2.0
  • Rear: 13-megapixel, f/2.0, 5-element lens and PixelMaster technology
  • Front: 5-megapixel, f/2.0
  • Rear: 8-megapixel, f/2.0, 5-element lens and PixelMaster technology
  • Front: 5-megapixel, f/2.0
  • Wi-Fi 802.11 a/b/g/n/ac, Wi-Fi Direct, Bluetooth v4.0, A2DP, EDR
  • 4G LTE, Wi-Fi 802.11 a/b/g/n/ac, Wi-Fi Direct, Bluetooth v4.0, A2DP, EDR
  • Wi-Fi 802.11 a/b/g/n/ac, Wi-Fi Direct, Bluetooth v4.0, A2DP, EDR
  • Wi-Fi 802.11 b/g/n, Wi-Fi Direct, Bluetooth v4.0, A2DP, EDR
Storage Type
  • 32/64GB internal storage
  • microSD support up to 64GB
  • 32GB internal storage
  • microSD support up to 64GB
  • 16GB internal storage
  • microSD support up to 64GB
  • 16GB internal storage
  • microSD support up to 64GB
  • 3000 mAh
  • 3,000 mAh
  • 3000 mAh
  • 2000 mAh
  • 152.5 x 77.2 x 10.9 mm
  • 152.5 x 77.2 x 10.9 mm
  • 152.5 x 77.2 x 10.9 mm
  • 148.1 x 71.5 x 10.9 mm
  • 170g
  • 170g
  • 170g
  • 155g

Actually, if you just consider the ZenFone 2 as a family of phones, and start identifying them by individual product codes (ZE500CL etc.) it gets easier to identify which ZenFone 2 is which. Except, of course, for the top-end ZE551ML, where both the 2GB and 4GB RAM variants use the same product code. While you could purchase the right variant at the telco outlet by double checking and asking the right questions, we would advise you to shop carefully when making such purchases online.

All 2GB versions of the ZenFone 2 are immediately available, with the the 5-inch ZE500CL costing S$249, the 5.5-inch 720p ZE550ML costing S$299, and the ZE551ML costing S$349.

The 4GB variant of the ZE551ML will be released in Singapore on 16th May 2015, with a price tag of S$429 and S$499 for the 32GB and 64GB variants respectively.

With all of that out of the way, for this review, we'll be looking at the upcoming ZE551ML 4GB version (ours has 32GB storage), which ASUS has been calling it a "Monster Performance Smartphone." For simplicity's sake, from here on out, we'll just refer to it as as the ZenFone 2.



The ZenFone 2 retains much of the design philosophy as its predecessor. The rear of the phone is ergonomically curved laterally (it's actually slightly more curved than last year's ZenFone) and fits comfortably into the palm of your hand, letting you keep a firm grip on it. While the phone is a bit heavier and thicker than many flagship phones these days, it's relatively compact and light for a mid-range handset, and still feels comfortable in hand. Size-wise, the 5.5-inch ZenFone 2 falls halfway between last year's ZenFone 5 and 6, which seems to have settled as the sweet spot for phablets, being large enough for enjoyable content consumption, and yet not too big to be awkward to operate one-handed. 

While the phone is still entirely plastic, ASUS has introduced a brushed metallic finish to the phone's removable back cover, which looks fairly convincing (at least at arm's length). It's probably not to everyone's taste, and 'metallic' plastic finishes always look pretty awful up close but, on the plus side, if you do hate it, ASUS has a whole range of optional back covers, ranging from multi-colored Transfusion covers to 3D-effect Illusion covers you can buy to pimp your phone (and you'll also find a number of other ZenFone 2 accessories over here). 

 The plastic back of the ZenFone 2 has a brushed metallic finish.

Removing the back cover reveals two micro-SIM slots and one microSD card slot (take note that the low-end 5-inch ZE500CL only has a single micro-SIM card slot). The ZenFone 2 supports Cat4 LTE, which provides data transfer rates up till 150 Mbps. However, unlike its predecessor, only one SIM card slot supports data transmission - the other slot is for calls only. The microSD card slot is located right above the micro-SIM slots, and supports cards of up till 64GB storage capacity. On our 32GB phone, after taking into account system files, there is a total of 25.53GB of total user space. It's worth noting that, despite the back cover being removable, the battery is not.

Remove the rear cover and you'll spot two micro-SIM slots and a microSD slot. 

Like its predecessor, the ZenFone 2 has three capacitive navigation buttons below the screen. Unfortunately, also like its predecessor, these buttons remain unlit, which can make navigation in the dark difficult. Below the navigation buttons is a metallic accent with ASUS’s trademark concentric circle design, which is a nice premium touch.

The most noticeable change for the ZenFone 2 is that the volume rocker has been moved to the rear of the device. We've seen this button layout before on LG's phones, first with the G2, and continuing with its subsequent releases. On LG's phones, the power button is wedged in between the volume buttons, whereas on the ZenFone 2, the power button can be found on top.

The problem with this placement is that it makes the power button quite difficult to reach while using the phone one-handed. Having said that, ASUS has also incorporated a double-tap function on the screen to turn the display on/off (just like LG's KnockOn) feature, so you may never need to hit that awkward power button anyway.

 The power button is located at the top of the phone, which makes it a bit awkward to hit.

As for the rest of the ports, the micro-USB port is on the bottom edge, while the headphone port is on the top, next to the power button, leaving both the left and right-side completely bare.


Display & Audio

This variant of the ZenFone 2 uses a 5.5-inch Full HD (1920 x 1080 pixels) resolution IPS LCD display, giving it a screen density of 403ppi. The screen is protected with Corning Gorilla Glass 3. Clarity is fairly good and color reproduction is accurate, although contrast could probably be a bit better. Viewing angles are excellent. 

Audio on the ZenFone 2 comes from a single speaker unit located on the back of the device. Sound output is rather average, and the rear-facing setup is less than ideal for any movie watching.


UI Features

The ZenFone 2 is powered by Android 5.0 Lollipop and runs on the latest version of ASUS' ZenUI. Most of the features from the previous version of ZenUI have been carried forward, which you can read about here: 5 notable features of the ASUS ZenUI

In addition, the ZenFone 2 gets some new features currently exclusive to it. ZenMotion lets you use gestures to quickly launch apps while the display is asleep. For example, draw a C to launch the camera, a W to launch the internet browser, an S to launch SMS messages, or an E to launch e-mail. ZenMotion also lets you flip the phone onto its front to mute an incoming call or any music playing.

SnapView is essentially a hidden user account where you can store anything you don't want prying eyes to see. You setup SnapView by creating a new lockscreen password. Whenever you unlock your phone using that password, you'll be in SnapView mode. Any pictures taken, or any apps installed or downloaded in SnapView mode will not be visible in Normal mode. Perfect for secret agents and anyone else leading shady double lives.

We've seen something similar on many phones now, but the ZenFone also includes a Kids Mode, which a parent can set up to limit the apps and functions the phone has access to, as well as the duration for which the kid can play.

View Cover Gestures

ASUS has also released a new range of View Covers for the ZenFone 2.


We saw these covers with last year's ZenFones as well, and they're back this year with some new and improved apps to increase their functionality:

  • Weather View: See current weather conditions
  • Camera Controls: Take photos without having to open your cover
  • Music Controls: Play your music
  • Flashlight: Turn on and off your camera flashlight
  • Change Modes: change the phone modes to Airplane, Do Not Disturb, Vibrate, and Silent
  • Check notifications
  • Clock
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  • Design 8
  • Features 8
  • User-Friendliness 8
  • Performance 8
  • Value 9
The Good
Great value for good performance
Decent camera
Quick Charging
The Bad
Average battery life
Non-removable battery
Power button is awkwardly positioned
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