[gbmor]

> Do sites need to explicitly support them?

The web site will need to support FIDO U2F, yes.

> Can I just use it for 1Password?

I've not used 1Password, so I don't know. The Yubico site should be able to tell you if a given thing is compatible.

> What do I do if I lose my YubiKey, are there recovery options?

Nope. Get two of them.

> Do you use it in addition to an authenticator app or instead of?

Sort of both. So if a site supports the use of an authenticator app but not FIDO U2F, I use the Yubico authenticator app. When opened, it stays locked until my Yubikey is tapped against my phone.