We went last year!
There's a supermarket through a gate out the back of the campsite and a few shops/pizzarias. The beach is probably 5 mins walk top. Not sure about the mileage to St Jean de Monts, but it was only about 10 mins or so in the car.
The pool was spotless and they were strict about shoes not going on poolside. There were several slides, a deeper pool and a shallower section for little ones. We had hours of fun in the pool.
Dsd (10) loved it there and made loads of friends at the park. Pretty bog standard evening entertainment, disco, kareoke, one of the bullride things (I opted to stay in the caravan as dd needed an early night!).
We liked being able to go for a saunter in the evening. There was a small market out the back of the site in the evenings, with rides for dd (3).
The beach looked nice ... but we did our usual of insisting we had to go to a site by a beach, going to look at it on day 1 and not returning (but we live at the beach in the summer at home anyway).
Anything else just ask! Who are you thinking of booking with?