From a reliability point of vieuw one should use as few as possible devices or components
in a redundant manner.
This is as far as I'm concerned the best way to evaluate what you should do.
Firstly
Radio manufacturers test their equipment using full equipped receivers with their largests
servo's (or at least they should do!!, anyway if they have any technical culture , and I
am confident they have, I believe they do).
So, if you don't use more servo's than your receiver can take, using no larger servo's than
your radio brand can provide, your ok whithout any power expander.
Usually RC manufacturers don't specify the amount and/or kind of servo's a particular receiver can
have don't they?

By the way, don't understand what the guy's above mean with "amplified". The servo signal is a digital
ground to rail voltage with a resolution of some 700 nanoseconds. Any decline in slew rate must be
corrected at the servo location. It simply cannot be done at the base of the transmission line.
Or isn't it the slew rate they mean.
Anyway, 1 meter simply isn't long anough to influence such a slow signal sufficiently important to notice.


Secondly
When you use a dual battery system to provide power redundancy, you should take care not to
overvoltage your radio components, so also DUAL regulators are mandatory (mostly to top on
6V) if your system can have the full battery voltage, only coupling diodes are needed.
One should be able to TEST both power circuits separately ( and here is a matter some
commercial expanders fail!!!!) so also dual switches are needed and a voltage monitor
NOT for eacht battery but only to monitor the receiver voltage.
You don't need a christmastree even if it has some sales aspects.
Note that diode coupled systems (most of the commercial systems are) require the separate battery's
only to have half the capacity needed because they are both in service.

In General

Avoid parallel servo's if you can but mix ( large receiver), then you don't need pulse buffering.
From battery to receiver use at least 1.5mm² wire and split it up in several standard
plugs you plug in y cables on the receiver.
Go for the heaviest RC-switches on the marked.

Look I know this is a very hot discussion and it is only possible to evaluate the pro's and the contra's after
a thorough and extensive statistical examination who is wright and who is wrong.( so individual experiences are worthless)
And by the way such an inquiry is virtual impossible and there for we are forced to electronically analyse
the situation because otherwise "safety" is more something that's between the ears than in the radio compartment.

Ground rule:more servo's than ports on the receiver need expander else not and simplicity and testability of the redundant parts