We chose Llewellyn Charters for a snorkeling excursion to Buck Island. Beautiful day, beautiful trip. I recommend this trip for any small group. For the most part he and his brother were charming and helpful. His self built trimaran is beautiful and a delight to sail on.
I most share one major caveat. Llewellyn was unable to fit my daughter or I with a mask that did not leak. As his frustration grew with being unable to fit any of his masks to us he became a bit unpleasant. I have used cheap masks before with no trouble. My daughter, a strong swimmer, later snorkeled on St. John with no problems using equipment from a beachfront stand.
I am not trying to slam Llewellyn, his excursion is a special experience but you might want to bring your own equipment if the snorkeling part is very important you. He needs some new equipment.