The guys using A123 -are seeing what we found out a coupleof years ago
Namely; forget everything you knew about other batteries .
All the redundancy and in line regs battery balance stuf is just more stuff to potentially fail
All JR stuff runs fine with A123 going directly into one of their rx. The "soft switch being the better approach
I threw away all the other stuff an use A123 for rx and power and ENELOOPS for tx power.
Also I use A123 in my old hand drills - no surprise dead batteries after they set for days/weeks/months.
Ditto for ENELOOPS in my Canon camera - always ready to go.
Charging two packs in a model is the only point of real possible confusion.
One pack MUST always be disconnected
A good charger (the FMA10 for example )uses three wires - per pack- it is to permit charge balance of each cell.
As long as you do this correctly - the BEST bet is just the most direct path from bat to rx

Because Ialso have models -planes and cars powered by A123 - I prefer a direct plug in setup - no power switches wherever possible.
My latest generation LiPos (40-50 amp cells) are great but the simple reliability and apparantly limitless number of cycles - The A123 remain a favorite.