I have one of these and I am convinced that someone would have to swallow it to have a reasonable chance of getting hit. I am on the side of the smaller powder charge, tight ball, and low hold. The muzzle kicks up something fierce. Lube up the lock well - the mainspring on mine isn't that strong, so cap detonation isn't 100%. All that said, it's kind of fun having that little cannon go off in your hand. And of course you should stand sideways, in classical dueling style.
Make sure you have a big, soft backstop. From 15 feet away you will be lucky to hit a 4' x 4' target area, at least the first few times. The rifling in the 2 1/2" barrel is kind of a humorous decoration.
Useless trivia: The manufacturer of the Lincoln assassination pistol was named Deringer with one "r." A newspaper misspelled his name in the aftermath of the shooting and the wrong spelling stuck. Even now the computer is red-underlining his name as a misspelling. Now you know.