I used the Reservation lane this morning.
I made my reservation back in February and there were plenty of time slots to choose from.
My reservation was for 8:20am (my choice) for a 9:30 flight. I arrived at the airport around 7:30, checked my bag, and ate some breakfast. The regular security line was quite long as others have been describing.I was flying Southwest if that makes any difference. The Reservation lane was a bit difficult to locate at first, but then I saw the flags up. I got to the lane a bit before 8:00am. I must have looked a bit confused, because a woman with a CLEAR polo shirt on started talking to me. I told her that I had made a reservation but that I was early. She asked for my bar code and she scanned my phone with her phone, then said I was okay to get in the line. There were 2 lines with one group in each in each line, and one TSA agent for each line. Once the TSA agent approved me, I quickly went to a line for the scanning/x-ray. The TSA agent there was a bit of a jerk, but that has nothing to do with the Reservation system. My husband who had pre-check was waiting for me on the other side but only waited a minute or two.
I think this is a great option. However, once more people start using it, I don’t see how it will be of much benefit. If there are a limited number of slots and no cost,it will become the next thing we have to wake up early to reserve x days out. Maybe the reservation system will have an extra cost at some point, but we will just have to wait and see.