I always bring a hand-held Garmin GPSMap76CSX with chip for the Blue Charts for the Caribbean.

It has helped save my bacon a few times.

One time the chart-plotter of the charter boat was simply wrong. It showed us driving across the reef at Marina Cay, when we were driving behind the reef. My handheld was fine. I simply ignored the chart plotter for the rest of the trip.

Another time when sailing out of St. Vincent our boat lost all power (eventually traced to a battery cable problem) and we navigated the rest of the day using the Garmin.

In other cases the boat simply didn't come with a chart-plotter in the cockpit, and the last thing I'm gonna do is go below when navigating in close quarters.

I trust my hand-held because I've used it for many years. Your mileage may vary with units that come with charter-boats.

Over the years I've found that most reputable charter companies are equipping boats better and paying more attention to this stuff.