My wife and I have used passport cards for a couple of cruises throughout the Caribbean and Mexico, and they work great. They cannot be used for international air travel, including travel between the US and Canada (my mom learned that one the hard way), or, if I’m a cruise, air travel from the Caribbean back to the US if you found yourself in the unfortunate circumstance. So they are a great (and cheaper) option if you know exactly what and when they can be used. If you are thinking air travel, a full passport is a must.