Giving this excursion 5 stars because it is well run and the people who work there are great. It is well-priced.
It's not for everyone BUT they do their best to make sure everyone has a great experience. You are divided into 2 groups - first group that goes are people who are comfortable with snorkeling/swimming. Second group is for those who haven't had much experience. There is always someone to ask for help and they are watching you closely.
However, I wouldn't go back because it was too crowded. You are guaranteed to see turtles, and all of the tourist boats are in the area vying for the same spot in the water.
Also, >5 people were vomiting on the way back despite all of the advice from the workers. Not their fault and it was probably a worse than normal day for sea-sickness. They were cool about it and didn't complain even though they had to deal with cleaning it.