I've seen the full OSIR carbon kit on a mk6 gti. cost comes in at around £1k for the full kit, but I think the diffuser is around £400. the front lip fits perfect, but the kit I saw had some issues with fitment on the skirts and rear diffuser. for that kind of money you want it flush.
I've been looking at getting mine wrapped for a while, but they have to be sprayed first for an vinyl wrap to be applied.