The Mico Flexilite is a tiny little unit with an integrated rubber 'tail' that loops over your bars to hold it in place.
With a single LED it was never going to be the brightest front light on the market, but it'll get you home in an emergency, and it has both solid and flashing modes.
Side visibility is surprisingly good, so you could even use it as a backup for a more powerful headlamp, many of which are almost invisible from the side.
It's small enough to slip into a pocket or saddle wedge (11cm from nose to tail), and fits in seconds to standard or oversize bars.
It takes a CR2025 lithium battery which should last 100 hours, but when it comes to time to replace it, the tiny screws on the battery compartment are a bit fiddly. The white finish marks easily.