I recently bought a genuine VW front big bumper to replace my after market one which was on the car when I bought it. I quoted the GPC price for a vw one to my local dealer and they said they'd match it (around ?120 I think). The non VW bumper was grey and streaky, the metal inner bit was very rusty (I've heard that this bit rusts out a lot quicker on aftermarket bumpers) and the whole thing didn't fit well. The new one is ten times better in looks, fitment and build quality. It is the same colour as the rest of the trim to.
Save up, pay the extra and stick with VW. Best bet in the long run.
