The AR stock type stocks are indeed hideous on a shotgun, but IMO, pretty is as pretty does.
I have a Knoxx SpecOps recoil reducing stock on my 870 Tactical, and it works well. The only functional issue is that it's a little difficult to get a good cheek weld- that results in inconsistent fit, which means iffy accuracy when you try to shoot clays with it. With large human sized targets at HD distances, that's not a real big issue- shotguns aren't precision weapons anyway (I'm not saying "just point it in the general direction," just that a couple inches one way or the other means little in that scenario, unlike when you're on the skeet field).
I might also recommend looking into stocks like the Speedfeed- they let you keep a few extra shells ready to go.