In all but one of alsqr's examples after doing a bit of research, you see these charges in combination with other charges such as felon in possession, drug trafficking, etc. The odd one out after a bit of bing investigation was a Snapchat video based prosecution where the guy apparently was issuing vague threats in the video and the NJ authorities claim that is was in conjunction with display of an "assault rifle" which is also illegal under NJ laws.
The multiplicity of charges is used to get a plea bargain on maybe one charge as the game for prosecutors is to avoid court unless it is a high profile case. Possession cases are simple because you either have the item or not and there is no intent issues mucking with your case. As most cases are resolved by plea bargaining, it is more or less an additional bargaining chip for prosecutors just as marijuana possession was for a time in many jurisdictions. This is one reason that the criminal justice statistics on convictions probably understate the severity of crimes committed. More or less, what I see in the pattern on alsqr's new stories is that mag charges are used as a tool to get "bad guys" that often are impossible to get for their actual crimes. I suspect that there will be a few "good guys" falling into the net but as a side effect ancillary to arrests/investigations for other reasons. Then the surefire fallback possession of an illegal item is used to induce a plea. This is basically how our justice system "works" with the elaborate constitutional protections reserved for those where a trial occurs.
Thus, as of right now, it appears that it is like seatbelt charges tacked on after other traffic offenses. That being said, I suspect that NJ authorities are a bit queasy about using that as a sole charge because the legal winds are changing as is the 2nd Circuit that could conceivably demolish much of NJ's tacked on gun legislation in a moment. While people harp on the 9th, in truth, the 2nd has consistently been the center of anti-firearm, anti-Heller court resistance. Also, the state is and has been widely criticized when it has picked up citizens from other states sojourning through it and NJ needs every buck it can get.
The irony is that NJ is probably one of the states, along with Illinois and Connecticut, that will have to declare bankruptcy in the not too long future and many of those enforcing the law probably will not see the whole of their promised pensions intact. That is to say that NJ will be forced to break its own laws and promises to its workers and I would bet that many of NJ's municipalities are not in much if any better shape.