Just did my first trip to Cozumel back in October. We stayed at Hotel Cozumel and dived with Dive Paradise.
I liked Dive Paradise and would go with them again. Our boats had about 12-16 divers on them, but they split us into two groups and staggered our entries so we never felt crowded.
The DMs were great and you could choose to set up your own gear or have them do it. Underwater, they allowed the group to go at it's own pace, as much as the current would let us do that. One person on our boat on vacation by herself chose to higher a personal DM as a guide and she appeared happy with his services.
We did loose two days of diving out of our previously paid for week-long package due to winds, and, per Dive Paradise policy, we were given a coupon for those dives on a return trip. We would have preferred a cash refund, but it is clearly stated in their policy and I believe this is a pretty standard policy, and not just on Cozumel.
We found a taxi manager in town who told us about Dive Shop Mexico on the mainland and we ended up diving the cenotes one of the days we were blown out. Definitely recommended! You just take the ferry to Playa del Carmen and they pick you up and drive you to the cenotes. They even provided lunch. Great shop and awesome experience.
If you choose to go with an operation other than Dive Paradise, that is fine too, as we saw at least one other op pick up divers from the pier at Hotel Cozumel.
I don't want to deviate too much from your original question. I can't comment on Dive with Martin, but if you have any specific questions about Dive Paradise or Hotel Cozumel, ask here or feel free to PM me.