Somebody at the local gun shows has been selling these things, and it could create a potential problem for the unwary buyer. You see, that's not an ordinary pocket holster. Thanks to the National Firearms Act of 1934, it's been imbued with special powers necessitating registration and taxation.
What makes it different? It's designed so that the gun can be fired without removing it from the holster. As such, it falls under the same restrictions as cane guns, Stinger pens, and the infamous H&K MP5 briefcase. Walking around with your gun in one of these is treated with the same gravity as owning an unregistered machine gun.
I'm not being snarky here. True, you've known me to be facetious in the past. It's a personality quirk of mine, but I am not being a snickerpuss here.
26 USC § 5845 (e) vaguely defines the concept of an "any other weapon (AOW)" as follows:
any weapon or device capable of being concealed on the person from which a shot can be discharged through the energy of an explosive, a pistol or revolver having a barrel with a smooth bore designed or redesigned to fire a fixed shotgun shell, weapons with combination shotgun and rifle barrels 12 inches or more, less than 18 inches in length, from which only a single discharge can be made from either barrel without manual reloading, and shall include any such weapon which may be readily restored to fire. Such term shall not include a pistol or a revolver having a rifled bore
The last sentence exempts regular handguns*, but the logic is that the handgun becomes a different device when its nature is concealed. This ATF newsletter [pdf] clarifies their thinking on the issue: if the holster conceals the nature of the weapon and the weapon is capable of being fired from within it, it qualifies as an AOW.
Now, does that make regular pocket holsters illegal? No. Those aren't designed to allow firing the gun without removing it, so they're not at issue.
There are holsters on the market that allow the gun to be fired from within, but they don't conceal the weapon completely. Those seem to be legal, if not advisable from a safety standpoint. It's the combination of features that makes it an AOW.
You can own a pistol, and you can own one of those silly holsters, but if you combine the two, you're manufacturing an NFA weapon. It's like Pop Rocks and Dr. Pepper, except with jail time. You have to pay a $200 tax stamp, file for a Form 1, and wait for ATF approval if you want to do it legally. Yes, it's really that absurd.
If you got shammed into buying one, don't stick a gun in it. If you should run across the guy who sold it to you, demand your money back, and inform him that he's placing people in potential legal jeopardy. There's no way he doesn't know what risk he's putting his customers through.
* When Homer Cummings drafted the NFA in 1934, he intended for handguns to be among the weapons registered and subject to a $1.00 tax. To quell opposition, the language on handguns was excised in committee.