I bought a couple and haven’t used them yet…also it’s been over a year since I read up on them (so take this with a grain of salt) but if I’m not mistaken they’re basically external storage that plugs into a usb port. A utxo is uploaded on to them. the signed utxo sits in external storage (offline and airgapped) waiting to be uploaded into another wallet (I think u can upload all or part of the balance/stored utxo)

That’s prolly a pretty rough description but I’m technically retarded and it’s the best I got without reading up on it. 🤷🏽‍♂️🫡