After reading the pdf above, I have to concead that the oem installation looks like a better design. You can see by the photos below that the third point on the draw tite transfers the towing force to the frame member that holds the rear wheel suspension (I guess its the axle).
While this design creates a strong and probably fail proof towing connection it may not give you the torsion support needed. It is attached to the car underneath the bumper (not visible) which might handle all the torsion support you need. Since I didn't install it, and I'm not removing the tupper-wear to see it, I don't know how much beef is there in those two contact points. If I were to to it again I would buy the hitch from BMW and install it my self.
Side Note: when I got this hitch, My wife and I made an impromtu trip to Key West with my Motorcycle trailered. I needed the hitch right now! the only place that could take me that quick was a trailer dealer that I have been dealing with for 20 yrs. He put me first in the que and installed it the next day. So my decision was somewhat of an impulse with little research
