I LOVE my logitech mx1000, although i dont love the shape, it can become uncomfortble after many hours of gaming, but that may just be, but if you compare the shape of the mx1000 to the shape of the.......i think the mx510? the 510 has a much rounder thumb slot, the mx1000 is sharper, which can be uncomfortable. you should try them out at the store, and play for six or more hours strait and see if its still comfortable, if not, return it and try another one.....also, the mx1000 is VERY precise, with a sniper rifle in cs:s it is possibly the best mouse you can get, i have never tryed the mx510 so i cant be shure though....