I used it when I was in college for my Senior Project. That would have been 1978/1979. I had a keyboard with the APL symbols molded onto the keypad.
There are a handful of modern keysets available with APL legends as well
https://novelkeys.com/products/cherry-olivia?variant=4300136...
https://21kb.com/products/21kb-apl-classic-retro-beige-keyca...
https://omnitype.com/products/gmk-dimensional-cyl?srsltid=Af...
Im running APL only stickers on my keyboard because it seemed more entertaining than blank caps for touch typing. Freaks people out, but really enjoy it.