[/INDENT]I'd rate my experience with it 4 stars, holding back on the 5th because of this. While it can help with situational awareness you can't trust it 100%. It's additive to looking over your shoulder, not a substitute. This disappearing act is especially dangerous when a car closes the distance behind you but falls back to your pace or slower because it's unsafe to make a pass. In this scenario the car could be hovering 10 or 20 feet behind you, but the Garmin is showing all clear.
You got me thinking about this. I guess to quantify what I think of this, I’d rate it as a 3-3.5 stars out of 5 for use with the Garmin bike computers. As a standalone system, I’d give it a 2.5-3 stars.
I think that the speed differential measurement and the loss of threats when speeds are identical is a fatal flaw (pun intended). It’s going to be hard for most users to keep this in mind and failing to remember or understand could have potentially fatal or at least disastrous consequences.
I take another star off for the standalone system version since it’s utility is dramatically decreased without the audio warning that you get when used with the bike computer. I, for the life of me, don’t understand why Garmin didn’t put in the same crappy little beeper they put in their computers - those piezoelectric speakers are dirt cheap.
But, it does help. Just understand it.