All of those boats have basically the same bottom. Not out of the same mold, but same bottom design. The RS has a bolt on windshield. The XS is the newer model of the RS, without the windshield and a few other changes. The Stealth is the newest model, with many style changes to the deck. There was a company building knock offs of the Stealth and calling the Ultras. That is why you may have seen some that look a little different.