Some of the catchers who play summer ball with us don't wear them, but the majority do. I'm a fan of kneesavers, as anything that can take stress off the knees is a good thing, IMO. If you think about it, the stress a catcher's knees are subjected to over many seasons has a little something to do with why many catchers can't run well as they get older, and if you can slow that down, why wouldn't you? Even if you don't like them for games, using them in practice and for bullpens is a good idea.
My own son has always used them and wouldn't think of giving them up. He also runs better than most catchers, 7.3 60 time. As for not being able to get low with them on, ask his mother when she washes his pants. His butt is always covered with dirt from touching the ground in his squat when no one is on base. Kneesavers don't stop you from being able to squat low, a lack of flexibility does, though.