I had never heard of A4Tech before buying this mouse, my trusty Razer Copperhead mouse had a rip in the wire and i needed a replacement. I bought a Logitech wireless mouse, which was a big mistake, although that's another review for another day. After which I bought this, It cost just under 30 quid, was wired so it didn't have any latency problems for games.
Ergonomically, it fits the hand quite well, although maybe not as good as my old Razer, but better then most alternatives. The buttons aren't too stiff like you get on cheap mice, or Logitech mice, and the wheel feels smooth and the click of the wheel feels just right. The side buttons can get in the way when first using it but shouldn't be a problem after a while. You also get a button just above the wheel which speeds up the response time on the mouse. For normal browsing i tend to leave it on green or orange and for gaming i set it to red.
Style-wise, it looks nice and the material is a sort of rubberised plastic, which means you wont get sweaty hand syndrome when using this for long periods. The mouse came in those impossible to open plastic packages and i had to use a pair of scissors to get it open. You get those quite a few of those rubber feet to put on the bottom of the mouse, which is considerate, as nobody else gives you spare feet. The length of the cable is about 2 meters which is OK, and it seems better made then the one on my Razer.
A big disadvantage of most gaming mice is that they do not have a wheel that goes from left to right, only up and down, and click. The extra buttons on this means you can live with that, although it would be convenient to have it on the wheel.
Software-wise, you get a program that allows you to change what the buttons do and assign macros to games/programs. This is quite useful for making a button do more than one action e.g. you can set that useless button near the left click to do a quick shoot burst, and reload. Or cycle through your open programs, the possibilities are endless.
Overall, i would recommend this for gaming or even as an everyday mouse even though it is quite dear, this is because it feels great in the hand, the buttons feel good to press, and it won't frustrate you like a wireless mouse can. After using this for about a year, the buttons still click only once when you press them as opposed to Logitech mice with cheap switches that click twice when you click them once.