Yes it stands to reason my electric bill will go down. And my gas bill will go up. I don't watch them close enough to tell. And with the winter we had here this year both utilities are through the roof.
But around here electric is more costly than gas-btu to btu.
Boiler mates are excellent. We installed on 4 heating seasons ago. Much less storage loss of but from boiler mate than w/ reg water heater. Not cheap. Google em and see what they say.