That depends very much on occupancy and how the occupants behave. I have had three here for many years and they work very well. However the technology is a bit basic, and I feel sure that we could design them to be better insulated so they can keep their heat for longer to cope with the up and down temperatures of this land.
Did you know that nobody has made a smart meter that can cope with economy 7 yet. I have been told this by several energy suppliers or as they really are, administration of bills companies. One might have thought that when designing such devices time related power usage would have been part of the spec.
As for the original question. How has this person got free electricity. Suffice to say that if this is true, you can jolly well be sure it will not remain free for very long as the government will want to tax it. Thus, to me I'd say, don't burn your bridges or count your chickens before they are hatched. Brian