Thank you, the Kong Cash notes were a labor of love and are now very limited in availability -- glad you got some! With Kong we wanted to create a completely new cryptocash from the ground up with Kong with the idea "what if a cryptocurrency started physical first". It was really a demonstration of the usefulness of secure element chips that generate their own keys -- work we've continued with Kong Land.
Unfortunately the chips we use for Kong Cash rely on the P256 curve rather than secp256k1. With Ethereum and the EVM we could bridge this via smart contract, however, Bitcoin script is too limited to achieve the same result (imo with good reason).
We landed on a very different chip configuration for Bitcoin which has the tradeoff of some centralized elements, but also allows the user to introduce their own entropy (unlike the chip we used in Kong Cash which in theory has very good entropy, but still relies on claims from the manufacturer). The timelock concept from Kong, however, works incredibly well for the Bitcoin Note as a failsafe for conditions where we disappear or refuse to service notes.