I have one in my Touareg and I put the control knob next to the dimmer controls on the left side of the instrument panel.
Unfortunately the steering wheel sometimes obscures the knob that has an LED in it to indicate the state of the unit. It can flash different colors to indicate braking, no load (open connection to brakes
While it works good enough I think that the Tek P3 is smoother and I like the brake current readout.
The Red Arc Tow-Pro fits in the Touareg better as I couldn't find a good mounting spot for the P3.