We use the passport app when we return via Atlanta. I believe it can only be used in a limited number of airports and one of them just happens to be ATL. Last year we made it thru immigration faster than the Global Entry folks did, but the arrival hall wasn't all that busy. Having said that, we do need to get Global Entry for when we drive to Mexico & enter back thru Nogales. That checkpoint is a zoo! I just applied & there are no appointments in PVD or BOS for months so I'll do it out in AZ when we return.