I'd want one if I got it for free and no NFA bullshit, it'd be a damn cool wallhanger, but it's not a shooter, and I don't want to pay tens of thousands of dollars for a potmetal desperation gun built quick and cheap with a very finite lifespan in mind, especially with ammunition and magazines not being widely available.
If I got to win that PSA Sturmgewehr in a raffle or something, I wouldn't mind it as a novelty, I could put up with small flaws which no doubt are insignificant next to the original's. The grade of metal can't be anywhere near as bad, so with enough gunsmithing anything is fixable. .300BLK would give me very similar ballistics to 7.92mm Kurz without having to scrape by for small productions of Prvi Partizan ammo or a magazine which isn't yet totally worn out.
Procurement was fairly dysfunctional in Nazi Germany, it's unsurprising that something wasn't done like it should even in the face of worsening odds. As the war goes, the noose slowly tightens and the window for addressing those kinds of things closes, and the potmetal part becomes a virtue because it's a usable gun that doesn't ask for much of the increasingly less available good steel.
I can only assume that the decision to pursue the Stg-45 was out of bureaucratic inertia or people unable to cope with how fucked everything was, there were some people who just didn't want to come to terms with how badly things were going and acted like all kinds of things were still within their means or a viable idea to pursue.
The way I recall the interview with HMG is that they claimed that original technical drawings for the Sturmgewehr existed and had defined dimensions and what not, but that they were lost or destroyed in the war, and that supposedly there might have been aspects left out which were filled in by 'tribal knowledge' from people involved in their manufacture, people who moved on and themselves lost to time at varying points.
That's HMG's claim, but it sounds plausible to me. Do you recall the video you saw, or at least who the other guys were?
They chopped down all kinds of stuff though, WW2 surplus was cheap across the board at the time.