RE: Cons for installing redundant receiver batteries ?
Using 2 batteries without a switch has the advantage of improving the capacity, you can simply add the capacities of both.
In case of a bad switch or plug connection or broken wire between one of the batteries and the rx, the other battery would safe the model.
If a cell shortens out (which odes happen) then the good battery gets drained and will not be able to safe your model.
So if I install a second rx battery, I will also install an electronic switch to separate both circuits. Inexpensive and lightweight.