With the plethora of "Mouse Guns" chambered in 380ACP, with a 6+1 capacity, and now many nearly as small 9MM pocket pistols, Derringers are outclassed for CCW and SD. But I think they do have a place as a fun range toy, and as a part of Cowboy Action events.
I don't have one right now, but plan to pick up a Cobra in 38 Spcl. Next time I see one in a shop, or at a show, and have a little extra $ in my pocket.