As I said, simply use and regular maintenance can reduce its effectiveness and eliminate it entirely
So, in that case, would it remain effective in cases where the gun was fairly new or hadn't been used and maintained much? If so, wouldn't it be worth giving it a shot and seeing if it ended up being useful in enough cases to justify continuing with it?
they just buy or use a gun that predates it
Yes. And in the same way, someone can buy a car that doesn't have seat belts, air bags, ABS, crumple zones, etc. If, like your friend, a person is stupid, there are stupid options available to him. But, notwithstanding those options, seat belts, air bags, ABS, crumple zones, etc., have saved millions of lives. Would the mcirostamps save millions of lives? Presumably not. Would they save enough lives to be worth the minor cost? I don't know. It seems worth giving it a spin so we can have the data to answer that question. If it turns out they're not helpful, we'd just be talking a few extra dollars on the cost of a few years worth of guns, right? That's not much to pay to find out if this might save a lot of lives.