RE: Power Expander or not -that's the question
Here's something to think about on this subject.
The Smart Fly power expander and the Spektrum AR9100 use basically the same curcuit for input power, it's 4 diodes that pass current through to the servos while isolating the beatteries from each other.
These diodes introduce a voltage drop. The voltage coming out of the servo connectors is about a half volt lower than what is coming out of the batteries.
While this is not the end of the world, you will find that your system consumes less power with the PE or AR9100 because the voltage to the servos is lower. You will also find your servos to be slightly slower and slightly less powerful than when sending power through a pure copper circuit.
TF