Publicity and free marketing for your cheap CNC business. Otherwise it seems a possible way to get a cheap CNC machine at a premium price. Other that what Lewis has written, I don't know the intracies of getting one's mitts on an AR-15 or why they're so desireable. Come the zombie apocalypse, I'd rather have a decent battle axe. Or for less apocalyptic scenarios, an AK or shotgun. Or if things are heading medieval in a hurry, a black powder musket. Until DIY printers and gizmos can print ammunition there's a big dependency on the availabilty of that, so primers, powders etc.
But generally if I wanted another firearm (former FAC holder) I'd want one that's reliable and dependable, which for me would show a preference for buying one from a gunsmith that knows what they're doing. Making improvised firearms and zip guns is nothing new.