Wife and I used the mobile app the second time yesterday at ATL. First time in January there was confusion as no one really knew where to go and there were very few signs. But when we finally found the one podium that had a scanner it was lightning fast. This time, we arrived into a packed hall and after asking three officials, finally were told to go into the regular line. We snaked back and forth for 10 minutes and as we arrived at the head of the line we saw that every podium now had scanners. The guy had me scan both of our QR codes from the phone, looked at the passports, then gave us the laminated card that said we were cleared for customs. However, when we got to the front of the customs line we had to again scan our QR codes and show our passports, even though the first guy said it wasn't required. So still lots of confusion. Hopefully after my June TATL flight it will be a little less cumbersome.