It is not a snorkel excursion per se, it is a coastal cruise and then they give you some swim time in the bay at Marigot, if one wishes to. I am one of those who will stay put.
Yes, I have heard "best snorkeling ever" reports from hubby and the others, but I am not a snorkeler. I have been there many times before and loved it. So just wanted to go for the ride.
Anse Chastenet is gorgeous. I am happy you have wonderful memories of time well spent.