I did quite a bit of research last year into puttin a bar on my MK5 and Towbars Direct got lots of good reviews iirc.
This is not a detachable bar though, so the neck will be on show all the time.
It's made by Westfalia who I think make some of the OEM bars for VW so quality should be good.
When I was looking at it, the best option seemed to be the Witter Quantum Detachable but it does require you to buy the 'GTI specific rear lower valance' from VW for about £50 which has a removable panel in it. Very neat and hardly noticeable when the neck is removed.
