I appreciate where you are coming from Robin, but you have missed one other critical piece of information which is high-lighted in red on the seat (other than the arrows and the cross): the tilt-release hidden in the 'cosmetic' harness cut-outs.
I am guessing this label only applies to 3dr variants as the 5dr has no need for the release mechnism (they might possibly be stronger as they have no need to tilt forward - or I am wrong and they are the same seat?!). This label is high lighting the danger of using harnesses with these seats because of the danger they will unlock the tilt mechnism. Part of the reason I raise this issue is because I can clearly see in photos that you have 3dr seats fitted RR.
I'm not out to shout you down or prove you wrong either. It's simply concern for you safety. I've brought this up on the forum because up to now we haven't seen anything official from VW on these seats - only the assumption that Recaro's statement regarding the aftermarket CS seat also applies to these (which is tenuous at best as we have no idea what corners are cut to keep the price down on the VW OEM versions). The harnesses also might be TUV approved, but they are only as safe as the seat they are attached too.
At the end of the day, it's all about risk. This is not something that could effect anyone else in a crash or even cause one (unlike illegal brake pads or chav HID kits). It's listed on your insurance, so that's a start. Where you'd get with a personal injury claim remains to be seen given VW obvious stance on these seats and ignorance unfortunately not be admissable as a defense. But all this aside, it's your choice.