We ("We" being spousal unit and two adult children) did the Cabana Rental thing January 2015 off the Fascination. A Lot of pluses to doing this and very few negatives.
Fixed location without being crowded by other cruise guests. Rental included loungers, shaded area, beverages and snacks. There is a lot to be said for not having to compete for shade, A/C, running water and waiters.
Can't really think of one. Okay. . . Rental is kinda pricey for a small group. At the same time, you are not stuck being right next to that group of passengers you don't want to hang out with. If you can join up with another group the PP cost for 6 to 8 (or more) is quite reasonable. It was really nice to have a place where where we could come and go as we wished, yet still be in touch with each other.
Either way. . . We truly enjoyed having a Cabana for the day. Hope you have the same experience.