Leaving the generators on all the time is an interesting idea. Right now mine shut off. I have the flow set at about 7 on each so I am already getting a nice purity as far as generators go. I have not had any problems with purity. I think the few minutes of lower purity at start up doesn't really seem to effect the overall purity that much when its mixed in with the volume of the 29 gallon holding tank.
I am always looking for something better though.
I have a good line on solenoid valves and it would be super easy to plumb and wire it.
I will have to give it some thought.