> For example, building a 12 gauge shotgun from 1" and 3/4" steel pipe is cheaper, easier, and probably safer/more effective than the plastic gun from the article.

Guns made from metal stock will probably always be more reliable and cheaper than plastic ones.

The issue is that a disposable plastic handgun is less detectable and will leave no useful evidence behind as it can simply be discarded at the crime scene.

(Of course, that's probably hogwash as a plastic feedstock capable of being a gun is probably going to be equally as traceable.)