The unit doesn't matter, the map does.. If you had a garmin GPS loaded with a topo map for example, you'd get all the land elevations and the outlines of the lakes..
CO can easily look your name up in the system as well.. Most guys aren't going to ticket you because you don't have the license on you (I've been checked a few times without my card, they took my name/info never an issue)
Even if your CC is compromised it's not like you'll ever be on the hook for the charges. Identity theft insurance sounds like an even bigger scam to me.