From the article:
“Mr. Keane and other opponents point to two early studies finding that the full numeric code could be read only about half the time on shell casings. In addition, they say, criminals could file off the code or replace the firing pin. And the technology would not apply to revolvers, which do not discharge cartridge casings.”
It would take about 5 seconds to file the tip of the firing pin. Or you could replace it...cheap - about $7 at Midway.com.
When Orlando Florida and some other localities started robo-calling businesses 20 times a day that put up the little roadside advertising signs, my first thought was to get some signs made with my competitors business and phone number on them, My second thought is that it would be simple to go to the local gun range and pick up some spent microstamped casings to leave a crime scene after picking up mine. What stupid idiot there are in gooberment.
In the versions of legislation that I've seen, messing with the micro-stamping is a crime. So if you have a gun whose paperwork indicates that it was micro-stamp when sold, and the micro-stamping is now illegible (whether from filing it off, or just normal wear), then you are in trouble.
To the gun grabbers, the value of this is that it provides yet another way to give legal troubles to gun owners.