I have seen advertisements for bumper pull type receiver hitch bars that have a cushioning element of one type or another, including cushioned pins that attach non-cushioned draw bars. The main claim is that this cushioning element protects your drive train during starting, stopping. There are also receiver hitches/rear bumpers that use some type of spring arrangement to accomplish the same purpose. Do these items accomplish this or is it advertising hype? What type of drivetrain damage could result? Most of my heavy towing is with gooseneck hitch, but do tow a bumper pull 2 horse trailer at times. 
