We chartered a 42 foot cat out of Key Largo a few years ago with a company called 360 yachting. We picked it for the reasons you mention, easy/cheap to get to, looked good on paper, but in the future we'd spend a bit more and go to the Bahamas.

Many issues with the boat, I think 360 yachting is no longer in business. More relevant is that we didn't find the area particularly good for chartering. Very shallow even a couple miles off shore made for non-relaxing sails, not many protected anchorages, marinas too shallow even for the cat, not very good snorkeling, and pretty mediocre restaurants in general. We had only 7 days so didn't make it all the way to Key West, so it might have gotten better the further we went, and we may have just hit all the wrong places, but just giving you our experience. We would choose another destination next time.