Hi Nualfaman, we went with the Westfalia option from Salop towing on our 159 SW. Got to say they did a really thorough job (it takes much longer to fit than on most other cars) and the result is good.
There's a small hole, but it faces the floor and you really struggle to spot that the car has a bar. the guys there were really good, I took my laptop and spent several hours using their WiFi to avoid having to take time off work.
My only gripe is the single 13S electric socket is angled towards the floor, for better invisibility. This makes hooking up the towing electrics a bit of a pain and I have to ensure that the cable is taped to the tow bar, otherwise it will (and has) scraped the ground, while on the move. An angled socket (if such a thing exists) would help.