sweeks

That technology is amazing. However, I'd still want to have a rear-view mirror so I could see if the approaching vehicle was actually a threat. I doubt the Garmin device can differentiate between a following vehicle with a 3-foot separation and one that's on a collision course. I'd be nervous relying on the flashing rear light to change the path of the approaching vehicle.
The video accurately cites the prevalence of "struck-from-behind" fatalities (from a study a few years ago by the League of American Bicyclists, I believe). The rider doesn't have a mirror... the cynic in me thinks this would weaken the sales pitch for the electronics.