I use em all the time. I have a tendency to get blisters on my thumb so they keep that from happeneing. I recomend them and for the price, you can try em and chunk em if you don't like them. And they just slide over your grip and sit next to the "collar" on the inside.
I bought a pair and put them on about a year ago. I'm kind of used to them now, but I can't really say that they seemed to help, but they certainly didn't hurt. Never had a blister problem, but I do occassionaly get a cramp in one of my thumbs.