Manta Adventures is a very organized and a safety first organization. We (mom, 12, 13, and 15 yr old) were very pleased with our adventure. Easily booked online and had all the instructions in email. Of course the fact that we saw the mantas certainly helped with our pleasure :-) I can't imagine going and not seeing mantas. We did not enter the water until just after sunset and were given 40 minutes in the water (maximum for safety with wet suits, I guess). Our family would have loved to stay longer (OK, my kids were probably done, but I could have stayed in the water for another hour watching that show). There was so much manta activity towards the end. There is no moving around, you hold onto the lighted float and just float and wait by the light. The brightest light is attached to the boat. But there are lights on the float you are holding on to as well. Mantas were there from the start to the end, fewer at first, then up to 3 at a time feeding. We went South to the Sheraton which I appreciated, because the prior 2 nights had no mantas by the airport. They seemed super conscientious to take the conservative route and go to the Sheraton which has a 90% success rate just fewer mantas and more boats in a confined area. Fewer mantas beats no mantas. Snorkeling equipment was good. I'd say great, but I had a little leaking under my nose (as did a few others), and I'm very experienced. But the masks were super clear, and that is what matters. No fogging whatsoever. They are super efficient to get everyone in the water quickly and watching once that sun goes down.
Now I do have to warn about sea sickness. The boat ride up and back is fine. But they arrive well before sunset, so you do have a long wait before you get in the water where the boat is churning. My 15 yr old felt a little sick during that time, but was fine once in the water. I'd say about 1/4 of the boat occupants were really sick. They did not look happy. Glad my daughter recovered in the water.