so in clarification.
Its supposedly completely legal
it can be shipped without ffl, and even using air freight.
it has no serial and is not registered and tracked in any way except when shipped from a retailer who cant track the individual unit nor distinguish what retailer sold it anyways.... so untraceable..
you get to most likely use a dermal or hot iron to carve out the rigger well.... so its 98.7% of the time going to look like crap and be an obvious botched job...
the concept of selling it after you transformed the hunk of crap into a "gun" is sketchy if not illegal.
(especially if you want/need a jig to drill it) AND it costs twice as much as hitting up our member with a gun shop who has been selling fully completed ALUMINUM forged receivers for $60.00, which will also be completely legit and no questions asked when you decide to sell it later, or when the general public or possible police officer or friend of a police officer at the range asks if they can check out your toy.
so in my evaluation.... and this is just my opinion; while there can be something said for the concept of "I did it all myself even the 20% that is "milling" the trigger hole..." this is marketed to criminals and idiots who want to over pay for hassle, sketchiness, and an ultimately inferior job done.