Friend of mine had one of these. He knew the guy that started importing them into Toronto or something along those lines. He used it all the time. Eventually the 407 matched his car to his plate from the times he went through without it. Got a bill for $500. He didn't mind though saying he probably actually owed them $2k-5k for the number of km he put on it.
His was designed in such a way that it was black when it had no power, so it would always draw a VERY small amount of power to stay clear. However, one time one of the wires came loose and it went black on the highway. He got pulled over. Cop made him cut the wires off and remove it on the spot and then snap it in half. At the time I think he said he paid $400 for it.