My favourite rear light this year is the Lezyne Micro Drive. It's USB rechargeable, and pretty much the brightest rear light I see on the street. It's so bright, other cyclists stop me to ask what it is and where to get it.
But it's not without its flaws. Google will tell you that these lights have a nasty habit of falling out their clip. One minute you are a brightly flashing red target for the vehicles behind you, and the next, you are some £30 short of lighting gear. This happens often enough that you'd think Lezyne would notice, and reengineer the clip. I've seen other riders resort to taping their Micro Drive lights in place with rubberised tape as tactical insurance against loss.
Today, I am surprised to learn that someone in Lezyne has access to the webs, and is listening to what they read. Lezyne have now made a much beefier clip, that is designed to stop your lights falling out.
Here's some pics of the old (left) versus new (right)…
I've no idea if the new clip is available separately, mine came with my replacement light…but it's worth finding one if you can, before it's too late.