We've used them for 3 different excursions and have had the best time on each and every one of them. 2 excursions were in Mexico (on the `08 WBPC sailing) and once was just last month in Barbados on the 11-Nt. Christmas Cruise. I highly recommend them!
If you're looking @ tours in St. Maarten/St. Martin, we did one last month there thru Bernard Tours. Not a dune-buggy tour, but what we did do was fantastic as well. I'd recommend them just as I'd recommend ShoreTrips.