I just bought a set of full length 12-28 briley companion tubes, and even w/ full choke tubes in my 12 they still rattle at the end when I shake the gun.(see my other post, i'm too dumb to link). I have not shot them yet so I can't give you much help, but I have heard good things.
A friend's dad has the el cheapo, knock-out-with-a-stick,20-28 and he shoots skeet w/ them, and really likes them.