I only have positive experience of the APC system.

Bearing in mind that 45mins in the immigration queue at ORD was previously deemed a success.

Oct - flew into DFW, used the APC - all ok, no cross on my white slip - 10mins max to get to luggage.

In between US trips at beg of Nov, renewed my ESTA on my existing (9yr) passport.

Nov 9th - Flew into ATL, used the APC - all ok, no cross on my white slip - 5mins max to get to luggage.

So, on my ATL arrival, I went thru with my new ESTA number without having previously had it manually processed. So far, I'm impressed.

The trick is to know where you are going and know what you are doing and not get caught up in the multitude of lines and quizzical looking pax that are aimlessly standing round looking around for divine intervention amongst the chaos of when a handful of international flights arrive at the same time..