I have the Knog Boomer as my back-up headlight and I also have the Boomer taillight as well. They are only single beam lights, but they are the brightest Knog offers. At 50 or so lumens, they are the brightest Knog offers. However, as a headlight, the Boomer is better just for being seen. It doesn't put out enough light to be of much use for road/trail illumination if you are going at a descent speed. The taillight, however, is fantastic. Very visible and lasts a long time. Here's some more info:
Knog Boomer Rechargable « Urban Velo