We used them while we were on AC over New Years. They are rumored to have a great set of scuba classes but we did not use them for that. The other function they serve is as a tour coordinator. They can sign you up for any activity on the island. However it was kind of a crap shoot as to who you got. We used them to book a couple of trips-- a Lamanai trip with (it turned out) Seaducded (great trip), a Hol Chan/ Shark Ray dive/snorkel, a Blue Hole Dive/snorkel with Amigo Del Mar ( I wrote about the Blue Hole experience in a thread called: "Trips to Atolls: one diver, one non-diver",
look it up if you want. An we also used them for a Mexico Rocks/Tres Cocos snorkel which had a great guide but a lousy boat--one of his outboards kept conking out and he rammed Ramon's dock when he picked us up.
Long story short, Blue Hole Dive Center is a convenience. You can arrange all the trips on your own, elsewhere, or directly with some of the companies (Amigo Del Mar or Seaducded for example). It was great to have everything planned and taken care of all at once, however, as I said above, it was a crap shoot. I would not go with the guy who took us to Mexico Rocks again nor would I go with the two guys who took us on the Hol Chan trip again (the Hol Chan trip had a great divemaster but a lousy snorkel guide).
To do over again, simply to have an idea of whom we were going to end up with on the water, I would not use Blue Hole again. I would book directly with whomever has the trip I want to go on.
Just my 2 cents. If you were looking for a critique of the scuba classes I sure didn't help you much!