We used Sunshine Flyer for the trip we just returned from and they were great! No complaints other than it's a pain to have to get your own luggage and go back up to cross terminals (as opposed to how easy it was with DME), but that can't be helped and has nothing to do with their actual service.
We waited about 10, maybe 12 minutes for the bus to arrive after checking in? Everyone was already there waiting so we loaded up and were on our way. They were clearly tracking our flight as we got a text as soon as we landed. We were the fourth stop so not as quick as a private service but no different from DME really, and they were as efficient as they could be getting people off and then to the next resort. Our flight back was 2:40, we were scheduled to be picked up at 11:05 (first resort out of 4 stops). The bus was there (parked, driver had run into the resort presumably for restroom break) when we walked outside at around 10:52. She came back to the bus and pulled it around for us by 11:00 and by 11:40 we had picked everyone up and were on our way to the airport. Plenty of time to check our bags, get through security, and eat lunch prior to boarding.