I have the factory fitted tow bar on my F31 - it's completely hidden from view when retracted. There's a button inside the left-hand side boot cubby hole and if pressed, the tow bar extends electrically from underneath the rear and locks itself into place - very elegant solution.
This is an improvement on my E91 where the tow bar was 'dropped down' half way electrically and then had to be locked into place by hand - at least the car came with a special glove one could wear to do this as the tow bar would always be very dirty. On the F31 the extension and retraction is fully electric all the way - much better.
F31 330d M Sport Tanzanite + heated Black Dakota
Pro Nav/Visibility Pack/Comfort Pack/Harman Kardon/Comfort Access/Adaptive Suspension/Tow Bar etc