I have heard rumors that some of the earlier ones may have been legislated against as "armor-piercing," but that later production differed and had been found by the ATF to be OK. Again, rumor-level reliability; I used to remember the details, but even then I did not have reliable documentation.
I can tell you for a fact that the later production is definitely not armor-piercing, armor being Kevlar in moderate amounts.
These rounds are very accurate in my 2.5" M19 and M66. They are rated +P. They shoot low, as would be expected of a very light bullet - I think about 2.5 revolutions (900 degrees) on the rear sight screw of a 2.5" K-frame. They don't drop much at distance. AFAIK
, PMC stopped producing them because the patent owner, Abe Flatau, came after them, and between the cost of not stealing and the modest sales, it wasn't worth it. They also made some in .44, which I wouldn't mind encountering.
I chrono'ed some out of my 2.5" Diamondback at 1446 fps; my 2.5" 19 gave 1387 fps, both with a standard deviation of velocity of 18 fps.