Welcome Jon,
I don't mean to be a nay sayer, but I will believe until shown otherwise, that system is now over priced and under efficient. PVs went up in cost. WAY UP!
"...if the spring runs dry or the cistern is full, the controller will shut off the pump..."
Now that means PV money not being used for anything, not to charge a battery, and not to not pump water that may (or may not) be needed.
When the switch shuts the system off, there is a $700 PV doing nothing at all.
LCBs are not free.
I believe a battery system is currently a better option. Not much different really, but a small battery and a tad more PV, balanced to the water needs.
ie. A 40W PV and 12AH battery with an LVD controller. It could potentially deliver more water per day for less money.
The 4GPM does not really mean a lot in this instance. My shower is 3gpm, but I do not use 4300 gallons per day, or 3,600,000 gallons per year.
G-