We loved this experience. The manta rays were beautiful and majestic and there's nothing like these gentle giants showing you their bellies and floating underneath you. So very worth it.
A couple things worth noting: the water is cold, even with the wet suits provided. Might be warmer in the summer, but we were shivering most of the time in the water. Worth it. Also, it was quite choppy. The boat ride is short (HUGE plus!), but not smooth and some people were even seasick in the water. It may have been worse on our tour - there were several mentions of how strong the current was that day - just be aware that it could happen.
They recommend snorkeling experience and we could see why - they move quickly to get you in and out of the water and have as much time with the mantas as possible. There are no lessons - you're just over the edge and in the water. Make sure you can swim! The deep water was unnerving to my husband (personal fear) but we never felt unsafe.
Last, I don't recommend renting the GoPro unless you have experience with one. I rented one having never used it before, and I found it distracting - I would have rather just watched the mantas with memories in my head than fidgeted with the camera as much as I did.
Our guides and driver were wonderful and knew exactly what to do to make sure we saw manta rays. The rafts with lights were awesome and they were all so knowledgeable - I definitely left with a new respect for manta rays! Definitely recommend this experience!