The lens (around 10-15€, depends on quality and diameter of lens) is glued directly to the soft bumper case (another 2-5€).

This is how close my cheap Samsung A3 2017 could get before:

And this is with the lens added:

So, it's barely new and innovative but it's combining two or three things lying around, so in my opinion this qualifies as a hack :)

Cheers, Jan