It's immensely irritating to find some bike light low on power right before heading out, and having to switch brackets because every light is incompatible. A few years back I settled on Cygolite and bought mounting brackets for most of my bikes, as well as for the family. This allows us to easily switch lights between bikes. We keep a basket of hotshots (100, 150, 250, etc) next to the charging station so anyone can grab one for their bike when heading out. Same for headlights, with cygolite metros of varying powers.