Shaun,
I have did a lot of research on this subject. Power only flows one way through the fromeco regulator. the ground is common. It is impossible for one battery to charge the other. On my 33% I plan on using a power expander like yours I love the way it has two deans connectors in parall so you can plug to seperate battery circuits into it with deans connectors and 18 guage wire. On my 28% i use two batteries two switches and two regulators pluged into seperate chanels in the receiver. 230 flights no problems, one battery does discharge a little faster than the other, but even after 10 flights it takes less than 2 hours for both to charge full. I do swap my bateries around every 50 or 60 flightss so they see the same cycle times. The batt share may have electronic redundancy but both chanels share the same control circuitry and the same output wire, even a wire can be a single point failure. Not trying to start an apples and oranges discussion just giving my 0.02.

Also I have a power expander for my 33%, How does your servos perform on 6.5v? I have never heard of anyone regulating them above 6.0v