While there are many firms that come and go in the PC hardware word (Vvikoo being one of them) XSR has always done it's best to represent the new guys as fairly as the more established.
Very high sensitivity; Perfect pin point accuracy; Easyshift is great for media and other uses; Sensitivity vocalisations are a novel touch; Easily the best looking mouse around; In-depth Macro abilities; impressive key remapping options
Expensive; No good for left handers