Great companion to B&M Cyo headlight
This light+reflector combo presents a powerful rear-facing signal to traffic coming up from behind. I find approaching cars give me a little more room and pass me a little slower than with my previous tail light (a 2" x 0.5" 2-volt red flasher). While the red-reflector portion has no lights behind it, enough bleeds down from the clear-lens top light to light it up a little brighter than my old light. The overall effect is - subjectively - 4-5x better visibility in daylight conditions. There is no flasher built into this unit: at first I miss this, but it makes sense that a flasher would make it harder for drives to gauge depth perception. B&M website has a good explanation for line lights & wide reflectors giving drivers better depth perception, vs point lights or flashers.
Kit includes a good long 2-lead wire with clips pre-attached at one end (for the light) and a pair of clips with heat-shrink tubes at the other end (for connection to the B&M Cyo headlight). Steel mounting bolts include steel lock nuts; bolts could be replaced with aluminum if you're brave enough to snap the cover off the light (I did not, at least for initial install). For the rack, seat, or seatpost side of the mounting equation you'll need your own mounting hardware.