Just returned from England via SEATAC and was prepared to wait endlessly for Passport Control. When we entered the area, there must have been 200-300 people waiting in a snaking line.
I had previously installed the CBP Mobile Passport Control (MPC) on my phone and filled in the information prior to our flight. Upon arrival. I completed the app as soon as I took my phone off Airplane Mode. This generated a QR code on the app for my wife and I.
When we entered the Passport Control hall, we approached an agent who directed us to another line.
From there we quickly approached another agent, scanned our QR code in and left Passport Control in a matter of a few minutes while all the other passengers waited for what must have been at least an hour.
This is great app!!