Ammunition aside (please!), the main problem with the old S&W breaktops is that they are old and use a lot of flat springs. Some even have a wild cylinder stop that curves like a mountain road and is about irreplacable if it snaps, which they have been known to do. I think it would not be good to try to use a gun in self-defense and hear "click". Highly embarrassing.
I strongly recommend against carrying any of the old guns for SD, even the S&W's, which were the very best. Other brands, like H&R and IJ are even more likely to have problems. Plus, many of the old guns are simply too valuable to risk having them confiscated and destroyed, a common fate of guns used in shootings, even when the shooting is justified.
Jim