Okay... but anyway, it seems to take advantage of low light running the battery at a lower voltage seems to be the better plan. That said if the battery+2V you spotted is correct, I will lose efficiency in high direct sunlight as the panel's MPP is 17V.
Mostly the question is about lead acid maintenance than solar charge controller efficiency.
I understand your scepticism though. I am the same about most home automation stuff. If I see a Wifi light bulb I will automatically assume it will come with and only work with the particular companies hub or controller app and avoid it.
This is why I'm doing it my way, as Frank would sign, home heating, solar charge monitor, whatever next. When I come to light bulbs and radiator controls I'll research for open protocol ones or build the thing myself... or hack someone else's to do it my way.
I don't see the need to feed everything up into the cloud either. "Here, have all my data, log all my personal behaviours and routines. Sure shut it down and brick all my devices or force me into paying monthly for the privelige of you deprecating all my stuff." </rant>