Backup, restore and U2F?

Can I use the backup and restore feature so that I can keep a physical onlykey backup copy, that I can still use for MFA with U2F? I haven’t used the backup/restore features yet and would like to have a physical backup that I can continue to use for MFA/U2F setups I have with my primary key, in case it gets lost or destroyed. I’ve been using my onlykey for a few years now, and it is awesome!

I think U2F would continue to work from a backup/restore on another physical onlykey, but am curious if I should update to latest firmware or anything before backing up and testing a restore on another key? I wanted to ask first before purchasing another one and attempting

You would follow instructions here to upgrade firmware - OnlyKey User's Guide | Docs

If you have firmware v0.2-beta.6 or earlier you would have to reregister U2F after upgrading. Backup devices will work for U2F.