I own several derringers and am completely comfortable with them. I do know that M2 is a derringer fan as well and have enjoyed his comments on the subject. The .410 round would make a mess of somebody. Might not penetrate very much, but pretty messy.
People are not wood. Try shooting a .410 round at bad breath distance into a brisket and see what it'll do. I have. I am sure that it would be quite a feat of superhuman toughness to still want to do harm to someone after taking one of those in the belly, chest or face.
I carry my derringer with .44 mag rounds in it. Hits 1100 fps with a 240 grain bullet.