Yup, my Serfas SL-255 has been my backup headlight since last year when a Light & Motion Urban 500 became my main headlight. I usually mounted the Serfas to the head tube, switching between two hybrids. I rarely ride the road bike more than 50 miles per session so I haven't needed a backup light on it.

The Serfas SL-255 uses a pair of regular AA batteries, carbon, alkaline or rechargeables. Replacement batteries are available everywhere, and I'd often keep a spare pair in the saddlebag on my hybrids.

At 255 lumens it's reasonably bright enough for a backup. More of a spotlight than flood so it's actually better suited to the narrow MUP to avoid annoying other users, but not ideal for most conditions.

Unfortunately I broke the strap recently by carelessly overtightening it. I need to buy a replacement. The old style Serfas strap uses a rubber that doesn't stretch much and a cam lever that can exert a lot of force. I was in too much of a hurry to adjust it appropriately and tore through the retainer strap. But it took a lot of abuse to do that, so it's not inherent to the design if the tension is set appropriately.

And the strap can be set correctly once and left on the bike. It has a really good quick release -- a shoe with a retaining latch -- to slide out the light and take it with me. Makes a pretty good flashlight too, brighter than my huge older Maglites, although not quite as effective as a persuader when used at velocity.

I may buy another entire SL-255, along with a backup strap, so I'm not swapping one light between bikes. It's a good value when on sale for around $25. Above that price, there are lots of USB lights that are better values.