Have been running Invisihitch for the 3 years along with Oem module and harness, it has been performing excellent. I would not recommend running aftermarket harness for few simple reasons; You will not be able to use none of the features oe module provides which seem small but make all the difference imo; PDC sound deactivation once trailer is attached, trailer lights fault dash display (don't do have go check all the light once you plug it your trailer it will tell you right away if one of the lights is not working) backup camera ball zoom when backing up, and most importantly safety DSC activation recalibration once trailer is hooked up. Although its a steeper price point in the beginning but in a long run and ease of use it totally worth it imo. If you want to save money can show you how; Recently I tried to add brake controller to mnie but bmw has discontineed it so I have decided to make my own using the same brake controller prodigy p2 used in their kit and make my own harness, real easy to make performs excellent towing track cars and it cost me $100 which is about $140 less BMW controller/harness cost; here is a diy how to make one if anyone is interested: