The 124-gr Gold Dot ammo that was marked "Not For Law Enforcement Use" was accidentally loaded with military-grade primers which were harder than commercial-grade primers. There was some concern that some police and civilian handguns which might have been 'tuned' for lighter trigger pulls may experience light firing pin strikes and misfires.
The ammo in question was part of a huge law enforcement contract for several police agencies within the United States. When it was discovered that the primers used were not within the contact specifications, the entire production run was disqualified.
The concern was the hard primers only. Not squib loads, not under-charged powder measures, not defective bullets, and not primers that would not detonate. There was a concern that it would perhaps require a firm firing pin strike to set them off. That's all.
For the most part, most modern (re: STOCK) high quality 9mm semi-automatic pistols will have no problems detonating these primers.
I bought several 250-rd boxes and have shot up most of it. Not once did I have a failure of any kind. If you can buy this ammunition at a decent price, and you put half of it downrange without a problem, you can bet your life that you the other half is as good as it gets.
For comparison, when Lake City military contract ammo doesn't comply 100% with the contract specifications it is sold off as "surplus" and not used for military issue. If the velocity is just one or two feet-per-second below the contract threshold it gets marked "Not For Military Issue".