I don't think they are very good with older cars. My S4 is pretty expensive when I get quoted from them.
However, with the '09 A4 for the wife, there was only about £50 in it, so just went with them. Now we have just got the '12 BE, and it looks as if they will be there or there abouts again. I will get the renewal next month likely, and we will see for sure, but on newer cars I think they are pretty competitive.
Couldn't tell you about service wise, but I should think they wouldn't be too bad. Audi motors as courtesy / replacement cars, Audi parts used, Audi bodyshops etc... Will all be helping for any potential warranties further down the line.