We dove with them a couple of times, but it has been about 3 years since. They were a good big operator with big boats (no six packs) They have a main shop which moved a couple of years ago (the old shop was located in front of the wreck of the Cali which was a nice shallow shore dive). I liked that they had a hang tank off the boat for the deep dives just in case someone came back to the safety stop low on air. At the time, they did not offer nitrox, but I don't know if this has changed. We did the west wall sites and stingray city (which leaves from snug harbor, next to the Hyatt, facing the North Sound)
I don't know about the diving in front of their new shop, but I would look into doing shore dives at the Eden Rock/Devils Grotto while you're in the downtown George Town area as these are the cheapest diving you'll find on GC. Also, if you have a car or you can take the bus up to the Turtle Farm and do the shore dive of Turtle reef mini wall with DiveTech. The shore diving on GC is great and by far the best deal on the island. You can easily double your dives and save serious $.