We just returned from Europe via SEA. Prior to the trip, I downloaded the CBM MPC app and registered our family.
When we arrived at SEA, the passport control line was LONG - a sea of people. We had checked luggage, and the line only grew as more people claimed their bags and joined the line. Then I remembered the app, and saw the big sign for “MPC” right next to Global Entry. I went into the app, answered the questions, took pictures of our party, and got a QR code good for 4 hours.
We were directed right to the front and waited less than 1 minute for the next agent. That saved probably an hour, at least. The MPC line was shorter than Global Entry, and it is free!