I've got them on my current GTD. I'm not sure they make a huge amount of difference and they're a bit of a pain to keep looking good (they tend to go white; mine have some
GTechniq C4 on to try and make them presentable).
If I had a red or a white car, I wouldn't have had them fitted, as they'd stick out like a sore thumb (like the black plastic door handles on the lesser Mark 5 models). As my car is Carbon Grey, they're aren't quite as obvious.