You probably know by now that Apple replaced Touch ID with Face ID on the iPhone X, which uses its True Depth camera to take a 3-D scan of your face rather than a 2-D image of your finger print. The recognition software learns more as it goes and is pretty good at ID-ing you even if your appearance is somewhat altered with a new hairstyle, facial hair, glasses, a different expression or what have you.
Not the first question Apple fans would have asked just a short week ago. Pairing the iPhone SE 2 with an iPhone X-styled notch seems unlikely, as the SE has typically been priced as Apple's entry-level 4-inch device. This hasn't stopped case designer Olixar from betting this year's iPhone SE update will be a radical departure from its current design.
There remains a large gray area and many pending court cases regarding search and seizure of smartphones by the police and federal agents. Currently you can not be compelled to unlock your smartphone and police need probable cause to seize it, but border agents do not. With Face ID however, it wouldn't be difficult for a federal agent to take your iPhone and point it at you in order to unlock it. Considering how much personal information people have on their smartphones, the heated debate between privacy advocates and law enforcement is not surprising.
While you could have many users with Touch ID, Face ID only works with one face, so each iPhone X can only have one user that can access it via Face ID. Of course you can always give your passcode to somebody to use once they've failed the Face ID authentication.