This is an exciting new feature in 1Password, and not to take away from AgileBits credit in any way for innovating, but it's largely a useless feature, due to no fault of AgileBits.
Most websites that support YubiKeys also require that a secondary authentication mechanism exist. Because companies dont want to deal with customer service issues when customers lose their YubiKeys and are permanently locked out of their data. So companies that support YubiKeys also have an SMS backup, Email backup, etc. And generally mandate such a secondary 2FA be set up.
Essentially this means security is only as good as the weakest link, usually SMS due to SIM swapping attacks, and the YubiKey is largely ceremonial.
One website I setup YubiKey on is Gmail and when I log in, it prompts me for it, but I click "authenticate another way" and then use Google Authenticator function, from within 1Password, to generate a 6 digit code, because it's far easier than getting the YubiKey.
If websites ever allow YubiKey to be the single source of 2FA then this will be a fantastic feature, although I never see that happening.