"The thumb grip sure looks like a good idea, but for some reason the plastic material here seems to make my thumb sweat more than usual - and noticeably more than the rest of my hand. I only noticed this while playing intense FPS games such as F.E.A.R. and PREY. I didn't have trouble holding onto the mouse, so the grip works, but I think it'd help if it were made from a different material - for instance, the same material that the right/left click are coated with. This issue is probably subjective."