That said, an old .25 pistol like the Phoenix Arms HP25A weighed 20 oz and was 5.5 inches long and 4.1 high. A modern 9mm Glock 43 subcompact is 18oz (22oz loaded), 6.26"x4.25", so what's the point of .25ACP when you can get a 9mm just as small? And better built?
It is usually the presence of a pistol and not its caliber that defuses the situation. Even very small pistols will drop someone if the pistol is used by someone who knows what they are doing. Most antagonists won't take the risk of finding out if the person brandishing the pistol knows what they are doing or not.
If you take a round from a .25, it's probably going to ruin your day.