After waiting 10 days for them to arrive and breaking 3 finger nails and shredding one finger removing the old vents, I now have my Audi TT air vents fitted.
Many thanks to Cryptic23 for his guidance on the ebay seller and hints on how to fit them!
A little expensive for a cosmetic change, but they look a damn sight better than the standard A3/S3 chrome ringed ones.
Part numbers (not sure why there are two) for anyone that wants to try it are 8J0 820 901 D and 8P0 820 901.
Will grab a quick photo when the light's better tomorrow.