Although I don't have a volume pedal, I can definitely tell you that the majority (all?) of volume pedals are "always on," meaning there isn't a switch that will bypass the pedal.
For your original question, I've heard the dunlop volume pedals don't suck tone, but are awfully big. They go for around $80-$100 new, depending on where you get it from. Speed TestScrabble Word FinderSolitaire