Good idea about the USB stick, I use several clients (is that the right word? Apps) and Damus has remembered it for me, although I’m preferring Primal these days, and I’ve written all those characters down on paper, but USB is easier
Discussion
Yes! If all your clients and keys are on the same device, you don’t have redundancy. I know several people personally who lost their Nostr profile because their phone got lost or stolen and they had never backed up their nsec. This can be easily avoided by copying and pasting it somewhere safe in a different place, or even writing it down on paper like you did.