Meuserna is correct; Krux operates statelessly by default.
But you can store a mnemonic in its internal flash memory or on an SD card. When you do this, you'll need to create a PIN. However, with Krux, it's not just a PIN; you can and should use a strong password to enhance encryption. Each time you want to load a stored mnemonic (and you can store multiple), the password (referred to as the encryption key in our documentation) will be necessary. In summary, if someone acquires your device, they won't have access to any unencrypted private information.
The "hide mnemonics" feature conceals your mnemonic AFTER it has been loaded. Therefore, if you leave your Krux on your desk, powered on, with a key loaded, an attacker won't be able to steal its secrets. Moreover, after the "auto shutdown" period, it will power off, thereby unloading the key.