The card though isn’t really storing in that product, is it? Seems like they are using the card as an authentication mechanism to go alongside (what I’m assuming is) username and device IDs to verify to what the app stores.

First thought I had with this was whether the app stores values or if it’s a “viewer” to that storage

Have had thoughts of seeing if it’s possible to provision one’s own flash memory (secure) chip + NFC as cold storage with a device as its reader. Kinda saw this as possible years back with NFC ring that someone did to clone their passport