I would assume that Face ID would require a clear view of the user's face...now how well would that work when lying in bed with half of your face buried in a pillow in the dark? Touch ID doesn't need to see anything but your fingerprint...and does it just fine in complete darkness without your face required.
Call me a skeptic but this just seems to be a more involved and difficult way just to unlock your phone. More secure? How so? What is more secure than your fingerprint? On top of that, you are allowed five different fingerprints to be recorded/stored on the device...just in case.
What is more natural than reaching for your phone with your hand, touching your finger to the Touch ID button, your fingerprint read instantly and your phone unlocked before you even look at it?
That's just my (skeptical) take on this new "feature".