The GPS model doesn't really add much if you already have a garmin. It will however link to certain samrtphones for a real time display, which I don't see a whole lot of value to.
Thus I went with the Contour HD.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.