I would like to share my personal opinion on the Huawei Ascend Mate,so before that let me refresh you with some specification. This phone comes with a massive 6″ IPS+ LCD based screen with 241 ppi, 2 GB of RAM, 8GB of internal memory, which you would have 4.03GB of space available after excluding the amount of space needed for the system usage, and the main point of purchase of this device, the 4050mAh battery capacity.
Let me start with the good side of this smartphone from Huawei. Well, this is how it started, I was thinking of a proper device to replace my HTC One, which was a amazing device with absolutely no problem at all, except for the battery life which was killing me softly as it could only last me up to 7 hours with my usage pattern. As I was looking into forums which most of the users suggested in order to get a better battery life, I have to root my phone and install a custom ROM which I could not perform as unlocking the bootloader on the HTC One would definitely void my warranty as the time i purchased, the device was already on hboot 1.54 which practically didn’t have an S-OFF which was still at the bounty stage. 
So, I have decided to sell it off and get a device specifically aimed to have a great battery life, and in order to get that done, I was reading almost everywhere and most reviewers and users mentioned that the Huawei Ascend Mate is a very good bet for a massive battery life. I was still reluctant to get a Huawei brand, as I was unsure about the after-purchase customer service reliability. But looks like the luck was siding me at that time as one of the online dealers was selling this device at a remarkable price of just RM999($303 USD) and with such price tag, I purchased it right away without thinking further. 
The phone came out of box with Android 4.1.2 Jellybean which was quite outdated as by that time HTC One was already running on 4.2.2 but it didn’t matter much as overall it is still about the same in term of performance in most ways. The Huawei Ascend Mate has it’s own skin which is known as Emotion UI which was version 1.5, and I realized the UI was almost the same as one of the custom ROM that I have used before known as MIUI which both had the most noticeable similarity of not having a app drawer. 
Okay, starting from here I would like to make it simple as it is getting longer and you might start to get bored.
Pros – Great battery life, could easily last me 2 days with 4 hours of screen on time(B221 official firmware), and could even last me almost 3 days with the Russian official firmware(B907), large screen with great speaker output (Dolby), very easy to install official firmware where you only have to depend on your external MicroSD card and lastly the 2GB RAM makes a huge difference with smooth user experience with very minimum lags to be noticed(B221).
Do take note that B221 is based on 4.1.2 and B907 is based on 4.2.2 an official Russian release.
Cons – Firmware, firmware, firmware. Yes the firmware that Huawei released for their customers are totally horrible as they have a beautiful piece of device with massive hardware but failed badly in term of software. What I am trying to say is, when I was on B221, I had major WiFi issues where I could not be able to reconnect automatically from WiFi to Data plan when the screen is off while the WiFi connection is lost. Most of the smartphones that I have used will be able to reconnect to any available connection as soon as it gets disconnected, but in this case the Huawei Ascend Mate still remains connected to the WiFi connection although I was already away from the location. You might not realize this happening as it happens randomly and based on Huawei’s firmware changelog, the B221  fixed this WiFi issue.
 So in order to get rid of this problem, I upgraded to the Russian firmware B907, which has a remarkable battery life, but yes, this firmware is worse because most of the time I could not get any of the push messages that I set-up on the smartphone. Another problem in this firmware is that you could not even play Clash of Clans with this B907 as it always ends up in a screen freeze and I have to manually force restart. Also surprisingly the 4.2.2 in this Russian firmware is not as snappy as the official international version of 4.1.2 B221. 
Some of you might not feel that those problems mentioned above is something to worry about, but trust me until Huawei works real hard on their firmware optimization, it would be difficult for them to be one of the top guns worldwide. There are very few custom ROMs available and most of them are still based on the official one with minor add ons, nothing is built from the stretch and even the leaked kernel source is still under-utilized. If solely based on battery life, it does have a great one as I am comparing directly with the HTC One.
Oh one more thing, you can actually remove the back case to have a look at the non-removable battery, just open up the MicroSD slot, and you can start pulling out the back case slowly, and I did this once out of curiousity and realized that on the battery it is written 3900mAh and also 4050mAh, which made me clueless but it might actually mean the total output would be just 3900mAh.
Want to know more about my experience or any tips and treaks related to the Huawei Ascend Mate? Feel free to ask me as I have done most of the things out of the available resources.