Although I can see your reasoning behind going with an authorized agent... you are essentially paying double for the same thing Revo are offereing. The fact that they will honour the VW warranty should tell you something 
Hypothetical question here: if your turbo fails, or a CV joint collapses, or your DSG breaks and your local dealer turns around and says 'not my problem mate, you've had it re-mapped', Revo will step in and replace those parts?
No they won't, and neither will the vast majority of the tuners out there.
It's such a grey area as IMHO there are very few issues that you could 100% say would not have occurred if the car hadn't been remapped.
I like my warranty but if your sensible and talk to your VW dealer you might be very surprised if you ever need to claim.
My old Edition 30 had a £1200 DSG mechantronics replacement warranty claim accepted and it was running Stage 2+ spec.