At the time he wrote it, there were not many hardware wallets with secure elements. Originally, the Cobo vault was recomended. Then the Cobo vault broke. Keystone is a fork of Cobo vault.

There are better options now. I would use a seed signer instead of seedpicker. There are issues with air gapped computers, but multi-sig mitigates these risks.

You could also use a Foundation device these days too.