Are you talking about just snorkeling in the family lagoon or doing the Seahorse Catamaran tour? We did both. We have snorkeled all over and have our own equipment to bring. We thought the lagoon was OK. Since we had our own equipment it was free for us. It's shallow and as is often the case in off shore snorkeling the water can get pretty cloudy when you have a lot of people in it. Too many people try to stand up & they kick up the sand etc. I recommend going out there early to do this before it gets toooo stirred up. We easily spent an hour out there just toodling around.
We have done a lot of snorkeling tours and thought the Seahorse Catamaran & crew were pretty lame compared to ones we've done in the past say in Hawaii or elsewhere in the Caribbean. They wasted a LOT of time on the dock before we ever moved and the check-in time was absurdly early. We easily wasted an hour just sitting around. Of course since we've done a lot of snorkeling we may have just been extra impatient to just get underway. I thought the crew was really of no value to anyone who might have been a beginner so thankfully we knew what we were doing & were able to just get off the boat and go. The little reef they took us to was actually quite nice and made up for their lack of interaction. It was a clear morning with calm winds so it was good weather for it. If we ignore the unfriendly crew aspect it was actually some decent snorkeling.
We really enjoy snorkeling so I would recommend doing at least one or the other while you are there.
In the snorkeling lagoon:
From the Seahorse Catamaran excursion: