All in all a stunning experience. As these kind of Manta Ray are only on two areas on Big Island and nowhere else in the world, it is basically a must do when visiting Big Island. The experience was great overall with a nice crew and of course with the help of many hungry Manta Ray a once in a lifetime experience. The maximum stay in the water was around 30 minutes, which is enough time to see the Manta Rays feeding on the placton again and again but not so long that you did freeze. Everyone wanting to swimm less than that had the option and help to go back on the boat at any time.
I would definetly recommend doing a Manta Ray Adventure, but honestly I do not think that the different comapnies hava many differentiators between them. Near our boat we had about 4-5 other boats also doing the adventure and it seemed all the same. You should definetly do the Manta Ray Adventure, but if there are no ticket with this company, I think another company will do the job as well.