My A4Tech X750BF came in today. After using it for around 8-12 hours, here are my impressions. Since my only other basis for comparison is the VX Revolution sitting on my desk, I cannot compare this mouse to some other high-end wired version (such as the MX500 or any Razer mouse).
Aesthetics: Plain and ugly. The red button and the lighted mouse wheel feel tacky. You most likely won't care. I certainly don't.
Build Quality: The components feel cheap but it doesn't feel cheaply put together. It's actually quite sturdy. I don't really mind this, as for the price I don't mind buying one every six months.
Comfort: It feels nowhere near as comfortable as the VX Revolution. By no means is it uncomfortable, but the design is standard and definitely doesn't feel heavy or contoured enough.
Compatibility: Plugged in and ran perfectly fine on Vista x64, no drivers needed. Which is great since no drivers were included (Vista not supported). I didn't bother checking their homepage -- there's a chance they might have Vista drivers there. As far as I'm concerned, all the buttons work without having to install extra drivers (which was NOT in the VX Revolution's case).
Performance: Great. No stuttering whatsoever, which was a serious problem on my cordless mice. Smooth movements up to 2500dpi.
Features:
The triple click button is nice but has been largely unused for me as I don't play Counterstrike. You can't exactly use it to double click either as it will open the file then highlight the folder, putting the file you've just opened in the background.
As for the software-free on the fly sensitivity button, I feel it would have been better as a slider or a switch. The way it works is there are six settings for every click ranging from lowest dpi (slowest mouse movement) to highest dpi (fastest mouse movement) and every click will cycle you through them till you start at the beginning again. This means a lot of clicks. This is not applicable in intense sniping or combat situations, and I suppose it MIGHT be faster to click six times every time you zoom instead of redoing it in your game settings, but it's a real pain in the ass. I see it being useful if you have a ton of time in a set sniping spot picking out targets. I personally don't use it.
Overall I like it and it's definitely the best mouse for its price I've found anywhere. I've found that the biggest negative against it is the comfort. Now if they could put the whole thing inside the VX Revolution's shell it'd be perfect.