My family and I did the Manta Ray Night Snorkel with Coral Reef Snorkel and Dive and it was by far the coolest thing we did our whole vacation (it probably makes the top 5 list of coolest things I've done my entire life). My family and I debated which manta ray snorkel company to go with, as there are several in Kona and we saw a few boats from the Sheraton Keauhou where we were staying.
I'm so glad we went with Coral Reef Snorkel and Dive because they took us to a place other than Keauhou Bay (they'd been having trouble seeing mantas at the bay that week). The location we went to was near the airport and is apparently a favorite feeding area for the mantas - we saw probably between 10-12 mantas, whereas I was hearing at Keauhou Bay your lucky to see more than 3.
Captain Ron and his First Mate, Roberta, also made the trip special. Captain Ron gives you a brief lesson about the mantas before you head out (including photos and names of a few regular mantas and how you can identify them). He and Roberta have been offering the manta snorkel for over a decade and have a genuine respect and appreciation for the mantas. Roberta goes in the water with you and guides you and the floating ring you hold onto to the best locations to see the mantas. She is an absolute pro when it comes to knowing where to be to get close to the mantas. We had several barrel roll within inches of us.
To top it off, Coral Reef Snorkel and Dive had one of the most competitive prices for the night manta snorkel. I've been to the Big Island a couple times now and this is the one thing I would recommend above everything else. You have to check out Coral Reef Snorkel and Dive - you will not regret it!!
General information about the manta snorkel: First, manta rays are completely harmless (unlike sting rays, they do not have a barb). As tempting as it is when they get within an inch of you, you cannot touch them. They have a protective film on this skin that protects them from bacteria and touching them removes this coating. They eat plankton, which is attracted by light, so the mantas indirectly go towards underwater lights. They are typically 12' in wingspan and will come literally within inches of you (but they will not touch you).
General information about the night manta snorkel with Coral Reef Snorkel and Dive: They provide you with a wet suit, diving flashlight, quality mask, snorkel and fins, a floaty ring that everyone holds on to in the water and towels for when you get out, in case you forget your own. They also have drinks and snacks on board - we even got homemade brownies made by Captain Ron's wife!