at the start of last winter I bought one of THESE from Ed Bike Coop and it's been great.
Specifically bought with the request "what is the brightest backlight you have?', following one too many close passes on Seafield & Joppa Rds.
came with three different attachment methods:
1. rubber band
2. seat post clamp
3. clamp that fits to saddle rails
for 2 & 3 it just clips in/out with no hassle. Same charging socket as my phone.
I bought an extra saddle rail clamp for a second bike.
on the bright flashy mode, its visible for miles - tested as I cycled to Moffat one evening and MrsMcR passed me in the car said she saw the light 'miles away' where as the other two I was running were visible only from a few 100meters.
Side debate about whether brighter is better - but on a busy road I'm going with 'yes', possibly not so much in town.
One plus I didnt realise until I googled it just now, is that according the Amazon this is a 'unisex light'. Who know there were male and female specific lights??