I use it on my weapons, it's not thicker than 2cm (it's about 1 and a bit), and haven't had any problems with my thumb and clashes of guards. There have been at least one or two that I can remember where I think the pad has made the difference between a throbbing thumb and no pain at all
Then again I don't know if I'd specifically go out to buy one. The ones I have I got as I was buying a complete weapon.