I don't understand the purpose of the two batteries and two switches...

The only thing I can think of is that if one switch would suddenly fail in flight (I don't know how), then you would fly on one battery rather than none, so that's a good thing.

For all other events it appears to not do much at all. Forget to charge a battery and you drain the healthy one. One battery shortcuts in the air, and you drain the healthy battery. Forget one switch and you have half the flight-time etc, etc.

I'm still all for one good NiMh battery, one good switch (protected from glow fuel) and a voltwatch that is visible from the outside of the plane.