FRiend, I have a Bond Arms SnakeSlayer that holds 2 .410 shells. I can assure you it is totally lethal from normal pistol defense ranges.
While rare, it IS occasionally my primary.
There is a plethora of effective firearms produced which are suitable for concealed carry/defense but in my opinion a 2 shot derringer is not one of them. As a deterrent, maybe. As an effective, versatile defensive tool, it is too limited. No professional would consider it. I guess we agree to disagree as the saying goes.
Only with buckshot or slugs, and even then, it’s a marginal weapon for self defense, imo. Certainly better than yelling, though!