My thinking about the auto controller is that then you get used to it doing the work... and unless you have two so it will do ph up AND ph down automatically, its only doing half the work... so its not even fully automatic...
its a very cool system, but when you control the ph yourself I would think you know more about where your plants are at, and what they are doing... for example...
if something is constantly raising your ph, and the controller lowers it constantly, isn't it like treating the symptom but leaving whatever is causing the ph to go up? the real problem?(as well as filling your plants with ph down solution?) so you would kinda need to control it yourself I would think, to prevent more problems, but this is coming from someone who is about to start his first hydro gro, so its all speculation on my part...