I think it's cool. Someone took the time to actually make this work. I see it merely as an exercise in pushing limits.
As for the "OH NO! PEOPLE CAN MAKE THEIR OWN GUNS!!" crowd. Anyone can buy AK47 lower blanks, dies, and parts kits to attach (with compliance kit), then bend the blank on a harbor freight press. Now you have an unregistered, no serial number ak47. And if you don't have the lower blank, the plans are out there to make them. Milled or stamped style. Tooling and parts would cost less than the 3d printing tools used here.
I haven't looked at how to do this for any other weapons, and this method I just stumbled on while looking at the history of the ak47 out of curiosity. I'm guessing you could build an AR15 in a similar manner.
But if someone wants to build a weapon, firearm or other type, there are is an unlimited supply of materials and methods. Tools and a brain are all that are needed.
Jesse
FYI: I have never owned, nor do I currently own any firearms. At the same time, I don't care if you do.