I have to agree with the general concensus above. I recently switched to Greenlight based on the generally high opinion of them amongst folks on here and the fact that they were £300 cheaper then Zurich (t/a VW Insurance) wanted for my Ed30, and that was inclusive of the Bluefin remap for which Zurich wanted a further £200!
I am paying pretty much what they quoted you. I think if you compare as others have suggested you'll find that's pretty good for a GTI - how much is the 'standard' premium and what extra are they seeking for the exhaust and wheels?