This thread is probably a bit stale but I figured I chime in.
I went a few years back on a shared boat with Vallarta Undersea and PV Scuba (seem to be out of business now). DMs from both shops were in a BP/W and had done some level of cave training in the Yucatan FWIW so there was no weirdness from the shop around that sort of gear. There were a couple of small operators with 6 pack boats and one large op with a cattle boat. Small was the way to go IMHO.
The diving was a lot like home but warmer--starfish, urchins, green water with maybe 15-20ft viz but 65F on the bottom. We did see a manta ray although the DM said they're fairly rare to encounter there.
The better sites are farther away and more challenging so don't be surprised if the op wants to see how you dive at a more boring site like Los Arcos (popular with snorkelers) before letting you book somewhere like the Mariettas Islands.
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