I reckon you will be about £250 for a service and would say you should stick to the dealer...
Thats what it cost me for the 3 year service plan. I took it in for its second service on Monday. When I booked it in I said I've noticed over the past 6 months that the drivers seat is beginning to sag at the back its like sitting in an hole.
They said seats aren't covered under warranty they are a wear and tear item. I said there is nothing worn or torn its just sagging. True VW don't cover seat coverings under warranty but any other defect is covered with the seats.
The tech came into me to ask about the seat he said he can't find anything wrong with the seat back. I said there is nothing wrong with the seat back its the base thats sagging, he changed what was written on his sheet. I also said that some tracks on the flash drive make the speaker in the drivers B pillar rattle. He couldn't make it rattle and when I played the rattly tracks it wouldn't.
After that the girl on the service reception said VW may ring in the next few days to ask how you have been treated would you mind completing this check sheet? There were 5 or 6 question asking how you had been treated. The second one was something like did they understand my needs I ticked Disagree because the tech asked about the seat back not the base someone had written it down on his sheet wrong. A said I Disagree with this part because the tech asked about the seat back. She said I wrote on the sheet seat base, so someone can't write or read.
Its going back in on Friday to have a new seat base fitted so it is covered under warranty.