I find it doubtful that anyone who does not already have an interest in the subject would watch this, and as such I find it disingenuous to rank it beneath six stars. If you seek it out, you'll find something of interest.
But the film is a weird paradox: It seems utterly focused on a single thesis (the cassette wouldn't survive without nostalgia) yet somehow meanders constantly (the sub-themes of that nostalgia are *all* over the place). If you make it to the end, you realize that nostaglia is maybe even a secondary theme to the subject of what I'd like to call "recreative labour." But it gets to that point very sloppily. And despite only being about 90 min, it feels like it goes on forever.
This is perhaps because the cassette inventor is at odds with the theme. He seems perfectly content with his life and memories and with being old but not only doesn't have interest in waxing nostaglic, he seems bemused that anyone else would.
As such, the storytelling sticks with that nostalgia far more than what *I* would have found interesting: how cassettes overtook albums as the most popular format, why eight-tracks failed in comparison, how long it took CDs to edge them out, etc. Etc. Etc. These are all minor details or storytelling casualties compared to the film insisting that you recognize "gosh, didn't we have something special here? Let's just bounce around from cassette aficionado or shopkeep to another with another random tale or tidbit. Then we'll go back to the inventor and see if his heart has softened any..."
That was what was frustrating for me: Any time the film picks up on an interesting thread, it drops it like a hot potato and retreats to the nostalgia subject.