Coverage of a recent criminal case points to the fact that Face ID while more secure in many ways is less secure when it comes to interactions with law enforcement.  The facts of the case as detailed by Forbes magazine are that officers went to the house of the suspect in Ohio on a child pornography case with a search warrant covering, apparently, electronic devices.  The suspect was the owner of an iPhone X.  The device was secured with Face ID.  The federal agent instructed the suspect to hold his face in front of the device to unlock it.

This then allowed the agent to access everything on the device:  chats, photos, email, etc.  It is not clear whether anything incriminating was found on the device.  Previously, there had been numerous cases involving Touch ID.  Those cases were not good for the device users.

This is in contrast to good old alphanumeric passwords, the longer the better.  Suspects, generally, cannot be forced to tell what their passwords are.  In some jurisdictions, they may face contempt consequences if they do not abide  by a court's order to tell their password.  There is a solid basis to regard telling your password to be testimonial and giving your password as potentially being testimony which is self-incrimination.  

No such protection exists in Fourth Amendment jurisprudence for use of body parts to unlock a device.  It is not testimonial.  Neither Congress nor the state legislatures has not stepped in to protect citizens from these attempts to access their private, personal information.  However, the U.S. Supreme Court has held that a search warrant or consent is needed to search a device, but the Ohio case involved a  search warrant.

If you are the type of person who believes that the government should not have access to your device, it might be time to disable Face ID or Touch ID on your device and stick with good old passcodes.  What you give up in convenience, you gain in security.