I got my first Exposure light in 2007 and currently have:
6 Pack,
Enduro
Race
Diablo
Joystick
Two Red Eyes
Flash & Flare
Separate battery
As you can see I’m a bit of a fan but I’ve finally given up on the FnF as they’re too unreliable. If the front plays silly burggers at least you can see it’s flickering. Unfortunately the rear is more tricky to monitor, and when you’re on the road, that’s always a bit of a worry.
I’ve re done the spring, tried normal batteries and they’ve been back to Exposure so I think I’ve covered all the standard ‘fixes’.
Recently got one of the Leyzne Micro rears and have been very impressed with it.
Yes it’s much bigger than the Flare but it works and there’s a better selection of modes. Haven’t used it on a MTB as yet but the mount seemed OK and duct tape is cheap if you’re worried about it bouncing out.
If you already have an Exposure light, I’d recommend a Red Eye, especially if you ride on the road. If you’re after a portable backup, then Leyzne imo.