Donnants is a superbly beautiful location and the waves are very consistent. Belle Isle is a bit difficult to get to. In summer the advice is to book a ferry well in advance to get a car accross to the Island.
Donnants is a sandy beach break which works best around low to mid tide on a small swell (<3foot) and mid to high tide on larger ones. Quite long rides are possible on the swells greater than 3 foot. There are several great waves that can be caught. Summer crowds of bodyboarders and bathers are a serious probklem except in the morning and late evening.
I recommend the excursion for anyone, as it's much better than most South Brittany spots I've seen....but try to avoid the peak season crowds.
coldswell.com