For what it's worth, this was posted on "another" website:
I just did this excursion last week and I can tell you to save your money. The main beach at Labadee is nice and much more fun that wasting you time and money going over to the Malfini Beach. They take about 20 people over in a small boat to this private beach that has some chairs and a bar. It's VERY small, no place for privacy, and they just keep trying to sell you drinks. We took the early excursion in the morning and were not in the mood for alcohol so eary, so didn't buy any drinks. After 2 1/2 hours, they load you back in the boat and take you back to the main beach at Labadee, which is where I wish we had stayed the whole time. Hope this helps!