Yes, I just want to chime in here, the voltwatch is indeed a direct measure of the voltage that the servos sees during action, and that is excactly what you want to see!

The flickering can be reduce by using a capacitor to help smothing out the deepest drops in the voltage, and prevent your rx to go into safe mode. Or you simply need to use a larger battery in combination with those particular servos.

There is noting wrong with the voltwatch itself.