Radios work okay as long as you don't have too many decks between you. All that steel can really mess up the reception. They are inexpensive so I'd suggest you buy you own set. The ship will rent them but this ends up costing more than if you bought them. There are many models and some are just FRS frequency, and others have both FRS and GMRS. GMRS freqencies have a longer range but it is actually illegal to use them without first getting an FCC license. No license is needed to use FRS channels. Instructions on how to get a license come with the radios. Of course, no one is stopping you from using GMRS channels without a license but they could. I imagine most people don't bother getting the license.
Another thing to note is that using these radios can be illegal in some countries, although I have never heard of the local authorities in the Caribbean stopping anyone from using the radios.
I have two sets. Both are GMRS capable, and yes, I paid the price for a 5-year FCC license. I think it was $80 and you can do it on-line. Midland is a good brand as is Uniden.