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The exposure bands ( not just a ring, admittedly, but still a band, I never take them out of their mounts just take the band off each time) work on the straps of my bag, thin tubes of my rear rack, stays, seatpost and up to the handle off my baby seat.
Having mounts for each bike even at £2.50 a mount would cost £35, and then I'd still have to remove them from the polo bike as they'd get damaged, and the track bike if I ever rode it on the track. And the handlebar bag on the mtb would require a different mount and the baby carrying bike would require different mounts for when the baby seat is on.
Sorry @chiroshi, this isn't supposed to be in response to your mount which I'm sure is great, but to the comment about bands being crap generally.
Bands don't really work for rear lights unless you're mounting on your seatpost. And they still require a mount, unless it's a knog-style or something really small. When I take my lights off when I get somewhere, I don't really want to have to carry extra bulk in the form of a mount + band.