On a recent AA300 JFK-LAX last Friday, was in J but the lady had an unwanted upgrade so I moved up to F. The floor, man, that's nasty. Other than that, everything seems okay, the lumbar pillow is really nice though. Not something I would pay extra for the onboard experience though. But, on that Friday, Priory check-in took me 20 minutes or more, while the F check-in seemed to be much faster. As others mentioned, it is just a regular counter separated by cardboard walls in the concourse, next to priority. The real First check-in was closed.