PP, here's our experience with Dive Aventuras. They were our first dive operation experience after getting certified. They went out of their way to ensure we had successful dives.
Dive Aventuras organization: They have several of the outboard motor type dive boats that handle up to probably eight to twelve divers. If there were enough divers scheduled they did appear to have the morning boats loaded according to experience level. The afternoon boats were more of a mix. If there were resort-intro dives or Specialty class divers onboard, they had their own DM. We dove the afternoon boats exclusively (our choice) due to our experience level, which was basically none at that point.
The reefs were all only a 5 to 10 minute boat ride. You geared up, got a thorough brief, and performed a back roll entry. We had no clue what a back roll entry was was until we did our first one there. Yeeeeeeeeeehaw.
There was a DM guide in the water with us on each dive, but no DM trailer. When someone hit the air mins and needed to go up early, the DM sent up the dive weenie and you performed your own safety stop.
As far as flexibility, they had a reef map up in the shop, knew which boats you dove during the week, and appeared to organize the boats during the week so you didn't dive the same reef twice.
We dove the Choc Mool / Kulkukan cenote. It was just me, my wife, and Mario (the guide). Choc Mool was interesting because there were a lot of openings to the surface which gave an amazing indigo blue tint to the water. It had a lot of limestone debris in the water that had fallen from the ceilings over the centuries. There were one or two "tight" squeezes, but I had no problem at all and my personal challenge is clautrophobia.
After 45 minutes in Choc Mool we were back at the entry point. They asked if we were cold and if we wanted to get out of the water. We were fine so they switched our tanks right there and we took off into Kulkukan, the second half of the dive. That dive blew our minds.
Kulkukan was filled with stalagtites, stalagmites, bacon formations, and fossils. There were more tight squeezes and again, no problem on my part. I'll see if I can figure out how to post pictures I took. This dive just sold us on cenote diving. We're diving Cozumel again in a couple of weeks and we left one day open to get in some cenote diving on the peninsula.
Dive Aventuras is a class operation. My brand new dive computer failed after my first dive and the dive shop set me up with a replacement console at no charge. We'll most likely go to the peninsula again in the late fall this year and will be diving with Dive Aventuras again.