cool. that's definitely a less difficult way to store your private keys. and it's foolproof since you're not transcribing anything from one medium to another. i think even normal cassette tape and a tape recorder if you don't mind speaking the seed phrase would work just fine.
i have never heard of audio cassette tape going bad in 20 years. i think it can last forever pretty much. these are ways that are way simpler than having to get specialized equipment and undergo a very tediuous and time consuming process. but to each their own
But I have a completely opposite experience and can safely say that I have seen audio cassettes become unplayable after a long time. Even if these cassettes were simply lying around and not touched. You see, magnetic tape has the property of demagnetization.
I am inclined to believe that there is nothing safer in terms of preservation than solid storage media. At a minimum, paper and a pencil, at most - a piece of metal and an engraver (or similar).