Mounting
It’s not all about the light. In fact, a great lamp is useless if the mount’s not up to scratch.
Look for a tool-free mount which is easy to install, particularly if you’ll be regularly switching the light between bikes.
Most manufacturers of commuter lights have got this sussed, and many opt for a silicone strap or o-ring to attach the light to your handlebar. Otherwise, many lights use a hinged cam-locking clamp.
A good mount will lock the light in place, ruling out any chance of it falling off when riding on rough roads, and, when riding on unlit roads, keeping the beam focussed on where it should be. Also check that the mount is wide enough to fit your handlebars.
