They were definitely only letting you use it at ATL if you'd been in before on this ESTA (they were quite brash about asking me "when?" when I said yes before they'd let me go to the queue for the machines!), so maybe that's something they've decided to do there to help split the queues while it's a new system rather than it actually being a restriction in the system.
The whole set of machines went down completely while I was using them, too. Got to the last screen and it refused to save or print, and then when I tried to attract someone's attention for help I realised it had happened to everyone. The system was rebooted in a few minutes, but it was still frustrating to do it twice! Then the queue to get asked the questions by the CBP officer meant that the time I'd spent in total, I'm not sure wasn't actually slower than just getting in the normal queue would have been!