I'll chime in here too, as I installed my OEM hitch 2 1/2 years ago. I paid $445 with my BMW CCA discount ($495 list price). There were quite a few steps involved in installing this hitch, but I would assume this to be true of any hitch. You definitely want the OEM wiring kit that comes with the OEM hitch. Installation was pretty straight forward and I've had no issues towing my track car over the last 2 1/2 years. The trailer pictured weighs about 4,000 lbs loaded up to go.
I just fail to see the attraction to "go cheap" on such a nice vehicle when the OEM hitch is so well engineered and integrated into the X5.