I did it on the Spree years ago but they have moved to Key West, their sistership the Fling is still going out of Freeport Texas. The Fling is a converted work boat with bunkbeds, not luxury but great diving, we did 4 or 5 dives a day :)
The Flower Gardens are very different from say Florida, the reef structure is different because you’re not near shore, the fish are confused, you’ll see many adults with juvinile colors. Besides reefs there are oil rigs which have become reefs, little fish around the legs and the bigger stuff just outside waiting for them to wander out. The trip will be much more diverse than a Carib island!