If you like to have a place to anchor your thumb, this thing is pretty cool. It is repositionable and provided both the cups and the surface are clean it seems to stay put. I deducted a star for personal feel - it's too big to be comfortable for me. I would have preferred something about half the thickness in both dimensions and a slightly rounded rectangle. But if the shape works for you, cool idea. I'd had a lot of "no-mod" rests, usually ones that fit to the screws of the pickguard of common basses. This will work on anything that has a smooth finish. Kudos, Thumb Fin.