Remember back when percussion revolvers were the latest . Many of these pistols were carried concealed and got the job done very efficiently , killed thousands of people. Funny how now a days some say these are poor weapons to conceal and carry.
Compared to modern weapons and ammo they aren't as good, and even though, such as my own which have been 100% reliable once I found proper fitting caps (Rem #10), there still is the chance that a cap can fall off, not be seated well and require a second strike, or get caught up in the action, as well as the ever so slight chance as with any revolver that an issue can happen (modern revolvers aren't 100% reliable either). And then I've read how the various springs used in these repros are known to break eventually often enough.
New springs, or better yet, replacement springs negate this issue, and maybe the cap issues mentioned might be about nil, it can't be 100% excluded. So far my two have been more reliable than several autoloaders, even ones of high quality such as Kimber, which was the most pathetic I've seen yet along with my father's Automag II before he realized AMT stated it required Winchester ammo. Regardless nothing manmade is 100% reliable.
And then there's the large cloud of smoke, which would become an issue I'd think indoors, and the fireball that would certainly mess with your sight in the dark. This can be an issue with a lot of modern propellants too, but the fireball is nowhere near as big.
Most people would prefer to use a HP, especially one that is bonded, though the old school 125 JHP in the .357 was so registering because it turned into shrapnel.
A ball seems slightly better than the average FMJ but still usually leaves a small wound channel. A SWC or WFN is much better but still doesn't create as much damage as a JHP, though it will out penetrate it. Of course this is if the soft lead doesn't expand, which is something I've pursued (what it takes).
I've considered having HPs made out of a mold and having the ram tapped for a pin, though this isn't really with CCW in mind.
Quite frankly a .45 ACP or .44 Spl with a modern JHP is superior
even to a SWC/WFN from our .44's. But I feel my 170 or 195 grn WFN is no less effective than a .38 Spl JHP+P and possibly more so, but then I'm also biased towards larger calibers and a SWC or WFN leaves a larger wound track than the caliber, which is why I'd take one over a ball any and every day. Handgun hog hunters use hardcast WFN boolits almost exclusively because of this (wound + excellent penetration).
All this to say a cap n ball is most certainly effective, especially with a larger caliber, but still isn't as nasty as the same caliber with a modern JHP. Useful? Certainly. As good as modern? Not really. But if this is a choice you make then consider the shortcomings.