I use a quarter turn tap on the input line and a pressure sensitive solenoid with a float valve in my reservoir in my system. This avoids the need to have power in my external RODI cabinet.
The only downside of this is that the solenoid is a little noisy when shutting off, but that’s ok in my situation as I only run this every 2-3 weeks. From everything I have read this is pretty normal for this type of solenoid. When I use the system I go out, turn the tap on, walk away and leave it to do it’s job and fill the reservoir. Once full I turn the tap off again. If I am home when it finishes filling the reservoir I will hear the solenoid shutting the system off and that tells me it is time to go out and turn the tap off. If I am out then it shuts itself off, and when I get home again I go out, check all is ok and turn the tap off.