Uhm, you can "pre authenticate" with Touch ID too in pretty much the same way (just using the home- instead of the side-button). But you also have the option to simply hold the phone to the reader without doing anything, which is what I do 99% of the time.FaceID @ checkout > TouchID
Rather than doing the authentication right at the same moment as purchase, you can pre-authenticate and once the reader is ready the purchase happens through your phone. With TouchID, if it didnt work for any reason this just took longer and held up lines.