Oh I am so glad you asked this!
We did this in April and we loved it! Really loved it!!! - and we are jaded excursion people, normally preferring to do excursions on our own.
They take you to Marigot for a stop off for about 45 minutes to an hour. Marigot was a goal for me to get to on this trip and it was nice to walk around and see the town for a little bit. Then you hop back in the very nice air conditioned buses to go to Grand Case. This is a stunningly beautiful little village on the water. I was in love with the pink sand beaches, the views and then we went out on the water in the semi submersible boat. The guides were wonderful explaining the fish - well, maybe a little rushed - but it was very nice when we went below to sit and see the ocean floor. It's a very short ride out into the bay in Grand Case and they spend a pretty good amount of time circling the outcrop and sending in a diver to feed the fish.
I loved seeing both Marigot and Grand Case on this tour. I felt the price was definately worth it as it was only slightly more than booking myself and we got a tour of the island both going and then coming back from the boat, plus a shopping stop.
Make sure you have plenty of film!
I think you will enjoy it. It was perfect for our children, a 1 yo and a 4 yo.
