I have two of these
and this as well
on the back and top of my helmet. They work great for rear vivability. I was out for a night ride with friends and saw how easy it was to see them over cars and suvs with this setup. Next is getting a white one on the front. Works great for aiming at pedestians who are too eager to jaywalk inbetween cars at night.
__________________
When sadness fills my days
It's time to turn away
And then tomorrow's dreams
Become reality to me