Originally Posted by
KLouis
Sort of semi-true. Most GPS devices can be "upgraded" by adding the necessary maps (not free, of course). GPS apps on smart phones do usually cover the entire world, though.
At any rate, as VidaNaPraia suggested, a GPS is certainly not needed in the Yucatan, and it has the added disadvantage that you always have to take it off your window every time you park your car somewhere where you can't watch it.
People have different comfort levels. I've not needed GPS and have driven extensively in the Americas (as well as Europe, Asia, Africa). I'm comfortable driving primary and secondary roads throughout the Yucatán peninsula (though I'd recommend a decent map, or perhaps a state map for Quintana Roo if confining one's driving there). But the single question the OP asked was about an unspecified Garmin GPS.
Definitely one would not wish to leave valuables such as a GPS in full view; it would result in a broken window and no GPS in short order. That's about the time you'll find out most insurance in Mexico does not cover glass breakage.