Hi,
Either the Eq6 Turbo or the Competition 12 Turbo would be good choices. Their functionality besides the servo matching on the Eq6 is identical.

1) You should never, ever plug a servo into the receiver on a PowerExpander or PowerSystem. You could overload the receiver regulator and take down your plane. You can use analog or digital servos with all our systems.

2) You can only charge both batteries at the same time if you have a charger that does high-side current sensing because of the common ground created. This is not unique to our systems. The only charger I know of that is not affected is the Fromeco Cube. If you want to charge both batteries at the same time with another charger or chargers you need to break the ground circuit by unplugging one battery.

3) The PowerSystems and PowerExpanders run both the servos and receiver off the same pair of batteries, but it does isolate the receiver from servo noise. If you run receiver and servos off separate batteries and loose a battery you loose your plane, there is no redundancy in this setup.