Hi Neil,
My wife and I just came back from the Habitat and it was great. The people and divemasters basically became your friends. Since all there is to do is dive you get to know everyone and the bar becomes the central meeting place at night. Very friendly atmosphere and the rooms are nice too. Food is OK, have had better, and have had worse. A hint, if you don't like one of their buffet nights, eat at the bar. You can go to town but it is expensive for a taxi and not alot there. The Habitat also has pickups for rent at about $60/day or $7/hour. They will load the truck up with tanks for you and off you go, all part of your diving package.
The 24 hour dive policy is great. The following day of your arrival you will have to meet at 9AM for an orientation and a shore dive. Boats leave at 8:30 so this is kind of a bumma. They do have afternoon boats when it is busy so you may be able to catch that, in our case they didn't but we were doing Nitrox Certification so didn't matter and we didn't have to do the orientation dive since we were diving later in the day with Nitrox anyways. As far as diving alone, you can do whatever you want on the shore dives, basically all the tanks are there and go diving. On the boats they will pair you up and if necessary make a 3 some. Do recommend you have a computer though as you get preferential treatment and more bottom time.
This is a divers resort and one of the few I would consider going back to. Very pleasant memories...