It was easy to fit (Apart from a few little things...)
1) Yes it does need an external antenna...
http://www.ebay.co.uk/itm/JVC-HAL-1...9?pt=UK_In_Car_Technology&hash=item3f1efc7d1d
This is what I used and it sits vertically in the windscreen. It's basically invisible from the inside.. (THIS WAS A BUGGAR TO ROUTE UNDER THE PILLARS AND TRIM!!!)
2) SD Card slot. Had to remove quite a bit of plastic to get the thing to go all the way back. Dremel realllllly is needed for this (I don't think I could have done it without it!)
3) Quadlock loom - It's such a tight fit at the back that I found the loom for the quadlock was stopping me from pushing the radio all the way back.
APART from these though it was a doddle! I also get a nice SEAT Media 3.0 Welcome screen which looks rather neat.
Absolutely Thrilled with the unit
Cost me £200 off the bay!