If it was just wastegate rattle then they could have been adjusted for £150!
I had my turbos done on Wednesday, cost me half the amount quoted above.
Would the warranty have covered my turbos given the fact I have Catless Downpipes, FMIC, Meth kit, Diverter valves etc? I dont think so. If the clutch went tomorrow, I'm sure they would say the same story, the clutch isnt designed to have 50% more power/torque running through it.
If you want a warranty, keep the car standard or just tune only.
if you plan to go further, then pocket the cash.
"You have to Pay to Play"
Car: 2010 Jaguar XFR (Cat-back exhaust)
Gone but not forgotten: Highly Modified E90 335i LCI M Sport Manual (circa 480BHP/500lb ft)