Yes, compared to a single battery of the same size. But putting two smaller batteries in parallel, compared to one larger battery, I don't see any gain.
A voltage drop over the switch, or the impedance issue, would both show up on the voltwatch as it shows the voltage reaching the RX when it is in use.

For a beginner with a 40 size trainer I still think that one good battery and a voltwatch is hard to beat, considering the simplicity and room for human error.