guys, it has been covered several times - only OE hitch... anything else will compromise the integrity of car-hitch-trailer (accessory).

most E53s are prewired for the trailer, the module does NOT need programming, it is for the light controls, also cuts off the rear parking sensors, and if you have user adjustable air suspension, it will NOT allow change in ride height when trailer is connected electrically.

installation is involved, so mechanical skills are needed...

again, only OE hitch...