Ah, it looks like their FAQ also says this is supported: Can I use the same Security Key with multiple Google Accounts? Yes. You can register the same Se

Ah, it looks like their FAQ also says this is supported: Can I use the same Security Key with multiple Google Accounts? Yes. You can register the same Security Key with multiple Google Accounts. https://support.google.com/accounts/answer/6103543?hl=en https://support.google.com/accounts/answer/6103543?hl=en