I have not gone out on a trip with Martin but I hear that the operation is a good one. Another one to check out is Pappa Hogs. They have 6 small/fast boats with wonderful personal service. Have a great time!
Our 3-couple group ( 4 divers, 2 snorkelers) "dove with Martin" in January '02. At our request, the 6 of us dove from a "private" boat. The driver took the snorkelers to a shallow spot inshore while the divemaster led us on our first dive. They ran us all in to a nearby resort ( deep water is very close inshore in Cozumel !! ) during our surface interval.
I'd forgotten how clear water can be until we dove Palancar Reef.
I'd use Martin again with no hesitation.