I have littles and it was nice to have the private space to put our stuff in the shade and hang out. Guaranteed shade for the kids. Plus it rained (hard!) off and on and the shelter was a nice escape.
We were one of the first off the boat and first to the cabana - I think we were in 16. It was beautiful and we had the beach to ourselves for an hour. That was fun.
The cabana has water and soda, a few snacks, fruit, towels ready for you. There's a private hammock. A cold outdoor shower to wash sand away. It's like having your own little (primitive) cabin steps from the beach.
A couple beach toys, bikes, rafts, tubes, and snorkel gear are included. Also sunscreen.
Bring sea lice repellant because we needed it when we there.
It's a nice treat. Certainly 600 is expensive compared with the experience. We are set to cruise again in May and won't even try for a cabana since we experienced it already.
The downside to the semi-privacy is that you are far from the activities, food, bathrooms (though new ones are almost finished) and there's a lot on the island to do and see. And we felt a bit tied to the cabana. Though we did take the kids to scuttles cove - the castaway kids club for an hour - and they did not want to leave they loved it so much.