The passphrase functionality is great, but reading trough the forum there is some confusion about it.
As default, it is “up in your face” and asks you for almost every crypto operation to enter it on the Trezor.
You can turn it off with “trezorctl set passphrase off”, but then you can’t use it at all.
Thinking about this; why not make an option “trezorctl set passphrase menu”, that instead of asking for the passphrase every time, it will be “hidden” under the decryption dialogs menu on the Trezor.
This will make it easy for most keys where no passphrase is needed (one click on the Trezor), but also add an option to use passphrase when it is needed. The “are you sure you dont want to use a passphrase” dialog that shows after no passphrase is entered can also go away in this case.