Changes
→U2F (Universal Second Factor) with Duo 2FA (Yubikey NEO and 4 only)
Program NFC NDEF text
The <code> -m </code> flag applies to the yubikey 4 as well. Use this to enable U2F. I do not know if U2F is also supported over NFC for the NEO.
For Duo, U2F devices can be self-registered, however it only can be used on Chrome. See the [https://wiki.archlinux.org/index.php/Yubikey#Enabling_U2F_in_the_browser Arch Wiki]