Interesting that they don't seem to have had much cultural impact. I've never heard of these, never seen them in war films. You don't hear songs wistfully using a wartime ocarina or referring to them.

Does this explain why all the kids in the States got recorders after the war? It's still a thing in 4th grade for most kids in public school.

Same. I was just able to order an original kit on eBay for $40, so demand isn’t high.