I find that when carrying the Hipster PDA in a pocket, the index cards curl up and get bent. However, it almost satisfies all my requirements for a portable note-taking device.
I just bend them the opposite way and they flatten out. For storage, I scan and OCR them, and then use a cheap index card box like this: https://a.co/d/hFOdEat
You need a rigid box. You can probably find something plastic or a metal box (like for mints), the trick is finding the right size (and/or cut your cards like me).