I can recommend this operation heartily. :wave:
I can't comment on the weather in Dec/Jan, I went in Nov--bring some warm stuff to wear both topside and in the water. I wish I had brought along my 6 mil shorty, that would have been the perfect protection. The water is 75-ish. The nights were comfortable, something like 60-ish degrees, it's good if you bring a sweatshirt-weight thing, and a windbreaker, and some raingear.
The days were perfect--80 and sunny and really nice.
The diving is pretty good, although the reefs are not quite what they are in the Caribbean, but it's all interesting. The corals are sparse on some sites, although there is lots to see. I saw some things there I had never seen before, like spawning damselfish. (that was cool). Lots of sharks, some turtles, and some sites had more game fish than I had ever seen.
The water can be rough, especially the crossing, so bring your Dramamine. I bailed in fact, on the crossing back at the end of the week, and flew to FTL from Bimini on a Chalk's seaplane. ($144 one way, ouch).
It's a good week, especially for the price! Go! Go! Shoo!