We've done this tour.
I agree with LisaK about "Hell". It's a very small rock formation that supposedly looks like Hell. We spent less than 15 minutes there. You will have time to send a postcard, but just barely!
We enjoyed the Turtle Farm. There's a guide who will tell you about the turtles and what they are doing to keep them from becoming extinct. You will also have an opportunity to hold a small turtle for pictures (your own). I think that you would be better off to hire a cab to take you to the Turtle Farm and pay the admission price (I believe it's $5.00) than to do the ship's tour for this.
The Rum Cake Factory is just a store that sells Rum Cakes. You can usually buy them on the ship on your last sea day for a discount. IMO, I like my own homemade rum cake better!