The Garmin 500 will give you all your data, including your HR, and it will add power picked up from an Ant+ compatible Powertap.
Why not just forget about the Garmin, and use Cycling Peaks WKO and the Powertap head unit?
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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.