The goal of the biometrics function is exactly as you have stated: to substitute the need for entering your secret and instead sign in exclusively using your biometrics, such as TouchID.
TouchID will fall back to asking for your secret if the biometric failed to identify you, such as if the fingerprint could not be recognized by the system.
If you're in need of more assistance, you can contact me privately via support@spectre.app, and you could consider including extra information available in Spectre's logs (shake your device after you spot something going wrong to bring up the logs screen).
