It is, especially if you rent a car from one of the vendors listed. It also is, if you are using water sports.
We're not divers, so we buy 1 for the two of us, and use it at the restaurants listed for free drinks, free desserts, 10% off the bill, free tee shirts, etc. I also use it for 5% off at one of the grocery stores.
With just a couple free drinks, it easily pays for itself.