AIUI Krypton is basically doing the same thing as these FIDO2 Security Keys, but their software substitutes an app on your Phone for the Security Key. So a web site offering WebAuthn can't tell the difference (unless you allow it to interrogate the "Security Key" to ask who made it, which you probably shouldn't)

I personally would rather have Security Keys, but a solution like Krypton is definitely easier for a lot of users and obviously the price differential is hard to argue with.