Summary: Good crew but extremely rude office staff that really can ruin a vacation mood.
I've manta-dived 3x in Kona. Once with a SCUBA team, and twice now on a snokel-hold-the-board trip like these guys, all with different providers. Ocean Encounters gets points for being a large boat and having a friendly boat staff, but the office woman makes me never want to go back or refer these guys, as there are plenty of others to choose from.
Full Review:
Unlike some of the smaller operations who might just paddle you out in an outrigger canoe, Ocean Encounters puts you on a large high-speed boat (with a bathroom) straight to the dive spot. This is probably best for most newbies or nervous swimmers.
The model here is similar to others in Kona: they drop you in the water and have you swim over to one of a handful of "surfboards with handles" that have lights on the bottom of them pointing down into the water to attract mantas. So it works well for people who've never snorkeled before.
On our trip, we saw one manta who circled between us and a few other boats. Obviously more would be better, but the Ocean Encounters boat staff did everything they could, and Rory and team were super friendly.
Negatives:
(1) The woman in the office was rude and short-tempered when we called to ask questions, raising her voice and cutting me off repeatedly at some of the most straightforward/easy questions, and
(2) we were shivering in the water (even with wetsuits), and it would've been nice if they'd have prepared some hot chocolate or hot tea for when we got out of the water (like some other Kona dive companies do).