Cornerstone -- Google Authenticator does present a problem if your phone stops working, is lost or stolen. Recovery isn't easy. I started out using Google Authenticator but stopped because I saw the writing on the wall if I ever was in one of those situations. It would be a nightmare if that occurred during tax season.
Authy is better in that you can backup everything with a password and recover all accounts if needed. You can also set it up on multiple devices. Authy also works everywhere that Google Authenticator works.
missingdonut wrote:How do you use an authenticator app when it's not native to the website?
What do you mean? Do you mean that the website requires that you use an authenticator app? Or that the website uses 2FA via text message?
If the former, you download a 2FA on your phone or tablet, such as Google Authenticator, Authy, whatever (there's about a dozen out there), you go through the process of setting 2FA up on the website and with the app, which usually involves scanning a QR code generated by the website with your authenticator app.
After it's setup, the authenticator app generates a 6 digit number every 30 seconds based on the original QR code given by the website (that only the website and the authenticator app know) and algorithm. When you login, you're prompted to enter whatever 6 digit number is currently appearing for that account in your authenticator app.