I did two two-tank dives, the shark dive and the scuba dolphin dive, with UNEXSO. The diving was decent. With Bahama diving, you don't get beautiful reef systems with lots of small fish; what you do get is big animal encounters.
UNEXSO is a very well put together, somewhat commercial operation. It doesn't really do the cattle boats for scuba, though that may be also because there just so many tourists on GBI that they can run boats of 40 divers. If they have enough divers, they're good about splitting up the divers by skill level. Though, when I dove Theo's Wreck, there was a girl that definitely shouldn't have been diving it because she didn't remember how to clear her mask and panicked at 80 feet. They have lockers where you can store your stuff and my wetsuit dried faster in their storage areas than in my hotel after I was done diving.
Shark diving was fun. They do a one-tank dive where you kneel on the floor of the ocean and their shark feeder feeds the swarms of Caribbean reef sharks that come by. One of the highlights of this dive is that the feeder actually put one to sleep and walked it up and down the line so that you can actually touch the shark.
The Dolphin Dive was great. UNEXSO has 17 trained dolphins; you go diving with two. During the dive, you get to pet and play with the dolphins. The trainers can get the dolphins to spin you around and kiss you, which is a very unique, fun experience. It's a little on the pricey side, but most trained dolphin experiences are.
Overall, I had a great time diving with UNEXSO. If I were to go back to GBI, without a doubt I'd dive with them again.