We have gone to the Reef twice by booking through autoprogresso when we get off the boat. I know that we will make it back to the ship on time because we ride the same bus that the people who book through Carnival ride. They are totally legit, and we save a fortune since we are a family of 6. On a side note, we went to Progresso on Dec 27th for a Christmas cruise and we tried another resort. I think it was called Technotel???? We booked it on land through autoprogresso and it was even less expensive than the Reef and seemed to be a little less "wild" (less drunk people :) They served really good food although there was a slightly smaller variety.
We always have a blast in Progresso. I don't know why anyone would want to miss out.