Works very well: I find that under heavy braking, as the bike's momentum moves toward the front and unloads the rear tire, it's quite easy to feel the rear tire slipping. (Common to all bikes without ABS).
So I've gotten in the habit, for urgent braking situations, of really squeezing the front brake and being light on the pedal. I mostly use the rear brake only to hold the bike on hills while stopped.
I've always found the rear brake pads wear faster than the fronts on the bike's I've ridden, so for long downhills, I never use the rear brake. This is especially true on the Empulse with its very effective regen braking in Sport mode, which, in first gear, will hold my bike to 17 mph on the steepest grades in San Francisco (20+%).
http://www.datapointed.net/2009/11/the-steeps-of-san-francisco/