I found out it's because links are going through a referral thingy called Skimlinks, must be to catch any referral fees (a good thing) - but it seems to break AutoTrader links!
The only issue I see with VW Finance on used is the higher interest (and missing out on things like service pack deals). The car looks standard in terms of options? On Drivethedeal a new 5dr DSG is £24,321 after discount, so definitely worth comparing finance on both, and as Exonian says any cheaper finance options for used.