It was a few years ago but Chankanaab sounds familiar. I think in my log i posted it as "Chicken Hab". As I remember it, it was very cave like, overhead still underwater, and still could see natural light (abet far away). It was a guided tour with dm's at front and back of group. Although they provided lights, I had my UK SL6 with me which was much better than the ones they handed out. (I didn't bring my 10w HID as back then it had a bulky battery the size of a base ball bat)
With the exception of when the dive operator through the ship in Hawaii had mechanical problems and the trip to Costa Maya I have always booked dives through the ship. If there is a screw up and your late getting back, through the ship they will wait, if you booked privately, your SOL.
Unless they have changed, the three cruises I did to Belize all anchored out. I understand it was about a 30 min tender ride into Belize City. I booked dives through the ship all three times. The dive boat came up to the ship, took us to the dive sites and back to the ship. By the time we got back to ship there wasn't that much time to run into the city. (not to mention I was tired and ready for a shower). So with three trips to Belize, I have dove there three times and never set foot in the country.
I would advise book thru ship.
In Roatan, Anthouny Key whom the ship used was nice setup, but I think there are much better sites than they took us to.
Grand Cayman, only did the stingray sandbar, so for me, been there done that why spend the extra money to see them again only using scuba. We also did Eden Rock once as a dive and once only snorkel. Where we were you could probably swim out to, but it was a bit of a swim.
On one trip Grand Cayman was first stop. We left Miami late as they were waiting for passangers from all over east coast to arrive. There was big snow storm covering NE. We then got to Grand Cayman late. There was a group that booked a private charter, they had the whole boat. I booked through the ship. Well due to the latness arriving we could only get one dive in. The guys that booked privately were still charged full price. When we got back on the ship, we were notified since we only got one dive in we got a 50% credit back.
That's another reason I usually book through the ship