DS and I have done the Shark Dive with SC. It was great. We booked it independent. They picked us up at the dock in a van. We brought all our own gear. If you need gear they have plenty.
SC is a large operation with lots of different dive options. The boats are not small, 6 packs, but they do provide good service.
They had us back to the ship in plenty of time. They are use to running cruise passengers so they know the routine.
IMO, The reefs around Nassau are okay, but nothing great which is why we did the special dive.
I would use them again.