This review is positive but detailed and a mixed bag, so read to through the end. Overall I had a memorable time and good memories, but due to my particular case it was not 100% positive. You will likely have a great time! So try it but read below to be warned.
The crew and boat and organization of this tour are excellent. The equipment is clean, the crew is very helpful and humorous, the boat and facilities clean and comfortable, and the snacks and drinks were plentiful. They explained what is happening very carefully and clearly and multiple times (which is very good in itself). We did indeed see many manta rays: beautiful, graceful creatures, and they come VERY VERY close to where we were snorkeling on the surface. I will never forget that feeling of seeing them swimming from the sea floor (easily visible) all the way up to the surface.
So why all the caveats and warnings above? First of all, if you get seasick easily then you are going to get seasick for sure guaranteed. I got a bit seasick on the way to the snorkeling zone, very much so on the way back, and got seasick bouncing up and down on the waves while snorkeling (you float on the surface of the ocean looking down through your goggles so you bounce up and down a lot, and since it is not in sync with what you are looking at you get dizzy: just like trying to read in a moving car). I wish there were more warnings about this: I get seasick easily, so this part was not so much fun. My younger daughter was like me quite seasick too, but my older daughter was not affected one bit and was happy as a clam. So it is really dependent on you.
Second, the spot where you can see the manta rays at night is on particular place in front of a hotel on a bay (they will tell you the fascinating story of why this spot is special and why only here etc.) But the boat left from another bay some 35 minutes north of the manta spot: so you have to take a 35 minute ride on a high speed boat (think bouncy) each way. If there is a company that operates much closer to the destination spot so the ride is shorter, I would recommend that. We left around 8pm and got back around 10pm and about 1 hour of that was just boating back and forth.
Now 1 hour with the manta rays was more than enough: it is hard to bounce around on the surface of the water and snorkel for that long anyways (I was unable to do so for more than 30 minutes that day). So that is not an issue.
Finally, a particular problem we ran into were these fire worms. The operators said it was our bad luck that the night we booked was the night the fire worms were out: apparently, according to the crew, they come out one night in August and so that was our unlucky night. They are not dangerous but very annoying: they are quite slimy, get in the way of manta ray viewing, and when they touch you it itches quite a bit (for about 4-5 hours and then it goes away). So imagine trying to view the pretty mantra rays while lots of these worms are floating around and zapping you randomly. Visually, they are quite pretty actually the fire worms, but it also did not help our experience. I would definitely call and ask to make sure you avoid this unusual bad situation.