Hi Maxamus,
Bluefin is expensive,around £600,but shop around you should find a 10% discount speak directly with superchips they should help you,my car has been Blufined for approx two weeks,results are excellent,read other comments before you make your mind up but personally i can recommend it,and the car now feels smother and more driveable lag is non existent,fuel consumption slightly better.
All i can tell you about your warranty perhaps speak to your dedicated technician at VW he will be the one that will gain access to your ECU in any future warranty work,see what he says if you know him well enough,even though Bluefin is reversable to standard setting it still can be detected if they need to read you ECU.
I know my technician, hes aware of my Bluefin and we are both happy with that
I covered my insurance some time ago on the site,my bluefin is down on my policy as there is no mechanical changes or cosmetic changes my insurance accepted it,the only cost is admin fee,but im lucky Bluefin is still very new so many insurance companies have not queeried to much about it as yet.
my advise is make sure you get it in writing
If you know your Vw garage well they may even fit Bluefin for you,for a fee but its peace of mind but get all the information first before you decide.
i hope this is of some use
