I was initially not sure seeing the Manta Rays in such a large group (around 30) would be a good experience. I must say the tour was very well run. When we checked in, they made life jackets available for the small children, issued snorkel equipment (including corrective lenses for those who needed them), and made wet suits available to those who wanted them.
My youngest son freaked out when he saw the manta ray. I late found out it was because his old brother had pranked him, telling him the manta rays are very dangerous (which they are not). I didn't know why my son was freaking out, but the moment I raised my hand one of the tour guides immediately saw it and swam over to help out. We ended up going back to the ship, but I did get to enjoy a few minutes of seeing the Manta Rays.
We forgot to bring our go-pro camera. Thankfully, one of the tour operators had a go-pro and took some video, and at the end of the evening she air-dropped the video to anyone who wanted it. There were no additional fees for this, which we thought was a nice touch.
You do need to provide your own towels, but other than that they have everything covered very well. Hot chocolate was also provided after the snorkel. This was the best-run large group snorkel tour that I've been on, so I'd enthusiastically recommend this tour to anyone visiting the Big Island.