Anything is better than nothing. Even a sap, knife or brass knuckles and I would prefer my Remington .31 over them.
The thing about setting off a pistol is that it tends to discourage anybody else from getting involved, and there is a little stand-off distance too. Using a sap or a knife or knuckles, folks may try to jump you from behind. PLUS if you can reach them, they can reach you.
I have a Pietta "Confederate Navy" brass framed Colt copy in .44. I cut it down to use in "pocket-pistol" side matches at CAS events. It has a 3" barrel. It's actually surprisingly accurate out to 15 feet or so, without a front sight. All I did was to square the barrel with a hand file after the cutting, and then used a coned stone in a brace-n-bit to restore a crown at the muzzle. IF I was going to carry this because I had nothing else, I'd use round ball and as much 3Fg as the chamber would accept.
Plenty of lead and the best velocity option.
Disadvantage:
5 shots (since one chamber is disabled to be a "safety" location).
Black powder in a short barrel, so some velocity is lost.
Single Action, so I have to thumb back the hammer each time.
Limited range as I don't have a front sight on the barrel, and it's short.
Advantage:
Better than not having a firearm of any type in an up close, lethal force situation.
Loud Noise, the opponent doesn't know he's being engaged with 1865 tech.
Small size, compared to Remington 1858, even in the shorter Remington configurations.
Much less expense than the 1858 if it gets confiscated, or most likely the idea that I will have to dispose of it.
LD