It doesn't take a rocket scientist. But if it takes a criminal, then only criminals will have these arms. The law-abiding, as usual, will abide by the law. And these arms will be all the more useful because the law-abiding have been disarmed. Criminals will have free play in the streets and homes of the poor.
Cheaper handguns provide more microscopic residue on the shooter.
Hardly a major concern for self-defense, but it makes it much easier to prove that the firearm in question was fired by a criminal who says otherwise. Criminals steal handguns. They don't buy them legally. The Department of Justice has already concluded that criminals prefer larger caliber, more expensive firearms. In other words, criminals don't use the very weapons these laws affect.