If this is the same tour, we went in 2015 (and will be on the cruise with you in December). It sounds and looks like the same one. Once at the island part, it was nice, but not anything spectacular. If it is the same place, the food wasn't great and the beach area was very small and not that accessible. There was a pool and a pier-like lounge area on the water that were nice. There were some hammocks and you could walk around a bit on the island. Again, nice, but not anything that blew our minds.
The big issue we had was the boat ride. On the way out, it didn't seem that bad in the speed boat because we were excited to be on the tour, although we did get pretty wet at times. However on the way back, the ride was very bumpy and we get drenched every time the boat smacked back down was not fun at all. The novelty wore off quickly and it seemed like the ride back took forever.
In my opinion, it wasn't worth it. It was cool to have the island area for our group and it is nice to say I did it, but knowing what I know now, I wouldn't have gone and my friend who was on the cruise with me feels the same way.