hehe...
It is ihnerent in the definition (the BROAD definition) of an AOW taht the ATF can pretty decide that almost naything is an AOW, if they try hard. A paper bag with a revolver in it, could arguably be an AOW.
The wallet holster falls into the category of an item taht doesn't look like a gun, but can fire rounds. In other words, you put your finger in the hole and the rounds can be fired, like magic, from the "wallet". As opposed to a gun case, which concelas a weapon, but must be OPENED before you can fire the waeapon. Theoretically, you couldpoke your finger into the paper bag and fire the gun, so it could be construed as the same type of set up.