RE: Goldwing 50cc Pitts Python V3.
On the "power expander pro" the RX power is regulated to 5.0 volts,, all the servos get full voltage from the battery, so you want a regulator if using lipos without high volt servos, I use A123s without a regulator.
Which one did you get?
I see no problem with the couplers,, they work for pull pulls