I remember in the .22 Apocalypse of 2013 where for whatever reason people thought because .22LR was impossible to find that meant somehow all .22 weapons were highly desirable, so people were selling their old .22LR bolt action rifles for $600 on GunBroker.
That and you have the opposite, multiple guys with a brick of 500 rounds of .22LR thought they had literal gold on his hands and wanted to trade it for a complete AR-15 or full size pistol.
I believe it. And they would appear to be cheap and easy enough to produce once they break. I’ve never seen those. I’m familiar with 80% lowers and even 3D printed lowers. Both of which are a pain in the ass and/or require special machines and tools. These things require nothing. Interesting. I might have to pick up a set when I get back to the states just to play with.
They hold up for range and other “light duty” purposes. I’ve loaned my molds to others and they’ve made reds and blues for their kids or grand kids. They think it’s super to have a red AR lower.
I switched to milling aluminum with the 5D jig after we used up all the resin that came with the original purchase.
I have a NIB Winchester 9422 that I could easily sell for $600. (But I won’t. 
)
Brownell’s is now making AR-18 style uppers for AR-15. They’re not cheap.