we didn't stay at the aire, we stayed at the campsite in the village itself, Camping Haliotis (Pontorson, France) , and found it quite good. the campsite backs onto the river and seemingly you can cycle the whole way to mont st Michel if that's your thing(4km). I think the aire was at the supermarket/filling station, quite close to the campsite, and didn't seem that appealing tbh.
the buses are free,and very well organised, and the car parks are massive. be prepared for a lot of people, even in June the streets were bulging, but it cleared the higher you went up. it's well worth the trek to the top.
P.S. during the week, the town/village of Ponterson is quite quiet, with most of the eating places closing quite early.
also there's a lot of building work going on just before the buses, with hotel after hotel going up, with your usual franchised eating places in tandem.
