J&B Tours runs a "native cruise" that includes snorkeling on the reef, snorkeling for conch, and a beach visit to prepare fresh conch salad.  They pick you up and drop you off at your hotel and provide all the equipment.  The equipment is reasonable quality.

Snorkeling on the reef is, of course, fantastic.  All the boats from the various operators seem to go to roughly the same area, so there may be little distinction between operators on that part.  Some guides do not join you in the water while snorkeling; and don't provide any particular information on the wildlife you may see yourself;  so no value added there. 

The conch snorkeling while interesting is fairly short.  You anchor in shallow water where they can be found, and scoop up an appropriate amount for your party.  This isn't really snorkeling as there isn't a lot to see other than the sand, rock and conchs, so don't think of this as another snorkeling stop.

Unfortunately most of the trip is hanging out on the beach and watching them prepare the salad.  On this trip J&B put ashore on the sand bar which not connect Iguana Island to the next island, so while they were preparing the salad ample opportunity is available to wander around and see the Iguanas on the back side of the island.  Many people snorkeled off the beach, but there isn't a lot to see there; your time is better spent on another stop on the reef.  The guides don't seem particularly knowledgeable.  In summary, nothing wrong with this operator, but might try a different one to get more snorkeling time and more information.