We were there in Nov '09 and used Hammerhead Sports, don't know if they are still around and don't remember if Sea Sports was available then. We were not impressed with Hammerhead Sports, didn't seem organized or very professional. We meet them in Belize City and had to wait nearly an hour for people coming in on another ship. Didn't see their dive shop, they didn't ask for C card, I felt like we should have asked the DM for his C card. I would dive with them again if they were the only thing available but know that you are on your own. I say that because I really liked the diving where they took us. We went to this manmade cruiseship people island called Bannister Island where we dropped off snorklers, then went just a little further where the reef was. Anchored in the sand and they said this site was Mermaid Castle, they could have just been making up a name. The 2nd dive they called Last Anchor or maybe it should have been "Lost Anchor" because the boat was gone when we got back, it had broken loose from it's sand or reef anchor. But I did like the diving, lots of soft corals, a short wall and spur and groove stuff which I have never done, kind of like diving in a ditch running through the soft corals.
Anyway, don't go out the gates into Belize City and make sure to pick up alot of Marie Sharps hot sauce if you're into that, it's the best!