back in May 2002. And then dove with them again because they were the operator for a cruise ship we were on (Royal Caribbean).
I would say that they are a pretty basic operation. They certainly don't go out of the way to impress you, but they're not unsafe, either.
You could end up on a boat with a bunch of snorkelers, though, which would mean you go to some of the shallower sites.
When we went back to Key West for a third time (again on a cruise), we dove with Lost Reef Adventures and felt we got a much more individualized experience (ie. we got to choose the sites we dove) and it was just us and another diver on the boat (this was late January, I think).
Your Mileage May Vary!