If we are talking about a "period correct" derringer versus modern clones (NOT strictly speaking, "copies"), let me point out that the original Remington O/U Double-D had one dangerous flaw: The ONLY "safety" was the half-cock notch. There was no other provision for keeping the firing pin off both cartridges. The oscillating firing pin was either pointed at the top round or the bottom. If the gun was dropped and hit the hammer spur, the chances were EXTREMELY HIGH that the "dog" would break off, and the gun discharge. This actually happened to a deputy sheriff down in Arizona. The resulting wound required amputation of his leg!
I am co-author of the book "Dr. William H. Elliot's Remington Double Derringer", especially the area of the mechanical aspects of this gun, so I reckon I know something about them.
I have never figured out how I could safely carried one with both barrels loaded! (Perhaps you could rig a leather piece on a holster that could be interposed between the hammer and the frame...as a holster maker, I could do that. But that's about the only way. I certainly wouldn't carry one the way Paladin did.) Most of the modern versions of the derringers, although they might resemble the original, have not only a half-cock notch, but a crossbolt safety that interposes itself between the hammer and the firing pins.
Had I lived in the 1880's and wanted a "belly gun", I would have opted for one of the S&W revolvers in .22 or .32rf, carried with one empty chamber. At the very least, I would have gone for a Sharps 4-barrel, with the hammer down on an
empty chamber. Yes, it would have given me only three shots, but that would have been better than nothing.
For modern usage, I would still recommend one of the .380 semi-auto pistols.