Not sure if the unit you are referring to is wired or wireless, so forgive me if this is not appliacable.
We used a Prodigy wireless brake controller on our 2006 Cayenne/28ft International with great success for about a year and a half, and really loved it. We recently moved from pulling with the Porsche to a Dodge Ram 2500, obviously with a "hard-wired" system.
The only issue with the wireless thing was not with the unit itself, but user error. As it needs to plugged into your 12v
in the Toureg/Porsche, one must remember to do just that...doesn't work very well otherwise. A checklist as we have all been encouraged to use really works, when you use it!
Happily we discovered our (my) error before mishap.
Again, we loved the thing.
If you would be interested I would sell ours cheap.
IM me if interested.