In general, I'd agree. However if you're using the 705 Head Unit to replace the SRM head unit, adding next to no weight, picking up some functions, and costs less than just the SRM unit, it seems like you're ahead with the garmin 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.