texlurch
Old fart on a hill
Maybe it boils down to the current capacity of the ACR. Can it pump hundreds of amps like the big relay, or just enough for charging? In other words, if the starting battery is dead, can the other one start the truck?
500 amp rating

I need to spend some more time on their site and see if I can learn more about it. It may just not be for me, since I like to keep it symmetric and not have an engine battery and "other stuff" battery. I don't have much other stuff.