I've had a few derringers and really enjoyed playing with them. Especially the mid to big bores. I only have one left, possibly the best of the best in derringer design, the old High Standard Double Action in .22 mag. It's double action addresses a couple of the single action's failings. The DA is much faster to get into action as it does not have to be manually cocked for firing. The same feature makes a much lighter trigger pull, but IMO in total, it's much safer as well. Don't know why someone didn't make a similar one in a larger caliber. It even has a wallet holster that allows it to be fired without removing it from the holster. I don't carry the gun, but wouldn't carry it in the holster if I did, thanks to the AOW law.
Many years ago, I did carry it as a back up before the small, light centerfire revolvers and pistols became available. From a practical sense, a two shot derringer makes absolutely no sense to me as a carry gun. For less weight and size, one can carry a handgun that is more accurate, faster to get into action, and three times the capacity.
If a derringer were all I had, I'd carry it, or if I wanted something to shoot shotgun shells for snakes, it should work well for that. I would concede that the big bores are fun to shoot. That alone might be reason enough to own one! There are no bad guns.
Savage