* Smart Card for OpenPGP (a super guide, there are [...])
* OTP on Android with NFC to replace the Google Authenticator
* Fido U2F for Google authentication
* As OTP authentication for Proxmox
Amazing is these features as Fido U2F, OTP, CCIC and SHA1-HMAC Challenge can be used at the same time and both USB and NFC is possible.
The small key is money value.