[salibhai]

What happens if you lose or break this thing and you have it configured on lastpass or google login?

[microtonal]

You can associate multiple U2F keys with a Google account. Since the Yubico's U2F key is really cheap (I think ours were ~15 Euro a pop), it doesn't hurt to associate another key and put it in a safe somewhere.

[godber]

You generate backup one time password codes at activation time. Store those somewhere safely. Use them in the event of trouble.

[girvo]

Backup codes, or you do what I did: I bought two, and keep one in a safe place.