I took the tour about six years ago and, if I remember correctly, it is the one where you kayak through the mangrove swamp and then do some snorkeling.
I liked it when I took it. The folks running it were pleasant, informative and helpful (including just plain island advice and directions). The mangrove swamp was interesting and kayaking very relaxing. The snorkeling was different than in the ocean, of course; the depth of the water was very shallow and the water still and clear, which meant you could see the water life extremely well. On the other hand, it wasn't a big coral reef with lots of big fish, turtles, etc. Still there was lots to see.