I have had some .38 derringers in the past. They functioned as expected. Every time I loaded and pulled the trigger they fired. I found the accuracy of my American derringer .38 better than expected. At 20 YARDS one barrel was 16 inches higher than the other. At 20 YARDS I could put all shots in a 55 gallon barrel. Recoil was harsh, but manageable, there was not a lot to hold on to.
I found it to be awkward to deploy, and slow to fire, but,,,,
For a gun originally designed to be used at 2 YARDS (the distance across a card table) a hundred years ago,,,,, I am sure it killed, and saved, a lot of people.
Does everyone remember the first rule of gunfighting. #1 is "Have a gun." I never had to use one, but I did not feel naked with one in my pocket.