A couple years back, a friend asked me to help him break in his new Kahr .45. (I no longer recall the exact model designation, but it was a compact size gun).
He has nerve damage in his arms, and firing more than a couple magazines of anything 9mm or bigger at one time is not something he can manage. He supplied the gun, and the ammo, I just did the shooting, and took the pounding for the 200rnd break in that was recommended in the Kahr manual.
That manual also gave a round number for the service life of the gun, I remember that, clearly, although I do not now recall if it was 4000 or 5000 rounds.
The gun worked acceptably well, there were 3 malfunctions in the first 200 rnds, all the same thing. Two failures to completely lock up during the 150rnds of hardball, and one during the 50 rnds of JHP fired last.
The one really noticeable thing (besides the strain -and some pain- loading the two mags over and over) was the "checkering" on the pistol's backstrap acted like a good high quality cheese grater on our palms. We did stop before blood was drawn, but it was a near run thing. A piece of black electrical tape on the backstrap solved this problem.
The gun has been shot a few hundred rounds since, with no issues of any kind.
Remember that these guns are NOT service pistols, and are NOT intended to be such. I found the initial 200 rnd shooting session to be both tiring and painful. (and I shoot handguns up through the big magnum classes). Taken for what they are, I like them, just don't think that that ought to be something that they are not.
As to buying used, vs. new, new has a warranty, used does not. If you know what you are looking at (and you do need to look), you can tell if used is a good deal, or not. If you don't, stick to new.