We're big fans of the new 2fer as a secondary or reserve light because:
--it's either a front or rear light with the push of a button.
--it's bright for its size: 60 lumens if used as a front light, 20 if rear.
--it lights up on the sides as well, which is what we recommend for all bike lights.
--it's only $25
--you can run the light steady or blinking. We strongly recommend you run the light steady, especially in the front and especially in the dark, because blinking front lights can cause a number of serious problems for people who'd like nothing more than not to drive into you.
--LED Fuel Gauge/Charge Indicator: Green = >75%, Orange = 75-25%, Red = <25%
In short, the 2fer is great to carry with you as a backup light, or get two as a secondary system.
Apologies for the music, but check this out