Derringers are for up close and personal encounters with for instance, a mugger, they're about the length of your driver's license and while I've never fired one, I'm assuming it would hurt like hell and be easy to blow a hole through your hand. I wouldn't expect to be able to fire this gun and hit anything more than 25 feet away.
Thats just from my limited knowledge, could be wrong, but I wouldn't want to shoot that damn thing. They are popular though, and have been since the oooold west.