Seems like a very good deal to me. MOTs are 50 quid each and major services are normally £329. You might want to double check they mean minor or major services because that deal seems to good to be true.
As for the quality of VW servicing, obviously they use genuine parts which is reassuring, but the workmanship can vary from dealer to dealer. I found a good one locally but as is always the case, complacency sets in, new staff come in and standards slip considerably, so make sure you dust off your complaining hat and use it if need be.....and tweet about your experiences because companies will only respond to bad press on social media these days it seems. If you email, phone or write them......you get blanked/shrugged off. A very public "You're crap" seems to oil the customer service wheels a lot more.
Anyway, if that deal is for 2 x MOT and 2 x 'Major' services......bite their hand off!