I also like the secret key feature, but I guess, if you set up an extra password for Proton Pass you can think of the Proton master password as your secret key. You'll only need it to sign in (similar to the secret key and 1Password). Afterwards you use the extra password (similar to the 1Password master password) to unlock your vaults. So even if, for example, a camera records you typing your extra password, you should be fine, as long as you have a high entropy Proton master password and a potential attacker doesn't get hold of a device that is locked but where you're signed in already.
I also like the secret key feature, but I guess, if you set up an extra password for Proton Pass you can think of the Proton master password as your secret key. You'll only need it to sign in (similar to the secret key and 1Password). Afterwards you use the extra password (similar to the 1Password master password) to unlock your vaults. So even if, for example, a camera records you typing your extra password, you should be fine, as long as you have a high entropy Proton master password and a potential attacker doesn't get hold of a device that is locked but where you're signed in already.