There are no regulators in the unit. It is meant to be placed inline with the batteries which inturn get connected to the (a) power expander system. Power is then regulated to rx and servos. The BMS unit simply measures and monitors battery status on a real time basis and keeps track of voltage, mah's used per flight, etc, etc. It can monitor nicads 5-12 cells and would see the a123's as 5 cell nicads.
This would show 6.6v's at both batteries. As you make flights you can see immediately how many mah you have used both per flight
and in total. Plus it shows both batteries simultaniously. This is the same as flying a few flights (as suggested) and then charging and noting mah used to determine how many flights you can fly between charges. Seems to me almost a must considering the characteristics of the A123's voltage curve.

I have one coming and will use with twin A123's. Results pending.