Based on this thread, I decided to buy one. I've had it now about 2 weeks or so. I leave the building tonight to head to my car and a coworker stops me to see if I have jumper cables since his battery is dead.
I laugh and pull this thing out. I initially tried hooking negative up to a fender but that didn't work so I hooked it straight up to the negative terminal and his car started right up.
I think I blew his mind when I pulled my Surefire E1B out of my pants pocket so I could see to hook the cables up.