ooga-booga might have purchased his after hearing mine chirp during rides
I believe the Varia is useless in trafficked environments. It would be so noisy that you will mentally shut it out. The boy who cried wolf. The only time I find it useless in traffic situations is when I am in the middle buffer lane, try to merge into two lanes and I do not have to constantly watch behind me for when it is safe to go. I'll watch my Garmin and finally look back when it says it is clear.
Works great in the open roads, like coming down a mountain road and you cannot hear well due to wind. And even it quieter situations, such as going up hill, you might hear a car, but the Varia will tell me there are actually two.
Mine has been triggered by cyclists.