I've got a few A4tech gaming mouse and a great supporter of A4 product..even bought the gaming keyboard and know the Vertex staff very well....And no, i'm not the salesman...

I've got 2 750B and BF but not the BK.

Good points:
Extremely accurate and fast, 3X fire button rocks, nice grip, nice price.

Bad points:
Quality inside not so good, is you open the unit you'll understand. Lots of button but some simply out of reach, the slim cables will open circuit after a while and soldering it back is not easy. The left and right buttons use omron switches but the scroll button push switch quality not so good, and its not by omron. Special snake skin tends to smell a bit like new PVC sofa covers.

Conclusion: For its price... GOOD...but if you wanna compare a G5 with a A4tech...better get the G5 For me A4tech X7 series is more like a poor mans gaming mouse compared to Logitec gaming mouse...but dun worry, its much , much better than the MX518.

X7 series is all good in the accuracy and speed but falls slightly short of the rest...especially the quality part. but again at RM100, its a steal (I bought my X750BF at RM150(special order), I think now its RM105)

BTW, for the new K and BK models, check out www.vertex.com.my contacts, sometimes new models come in months after its advertise on the A4tech Website.