There’s one big conceptual difference between Face ID and its predecessor, Touch ID. With a fingerprint, you have to explicitly touch the home button to confirm an action. When unlocking a password-protected app, or unlocking the iPhone itself, it’s hard to do it unintentionally. But what about buying an app? The old Touch ID way is to tap the buy button, and then use your fingerprint to confirm the purchase. What happens with Face ID? How do you cancel a purchase after tapping buy? Do you look away? Close your eyes?
No. It’s much simpler than that, although much less discoverable than touching a fingerprint scanner.