I suspect that this sort of device could be removed by the power company should they discover it.The homeowner/tenant does not, in most cases, own the meter and some power companies could consider this a modification of the meter and have it removed. Heck, they might even bill you for the removal. I'm speculating, of course, but it seems like a real risk to me.
I can only imagine the look on my meter reader's face if he saw a device like that attached to the meter.
One would hope that Wattvision launched(s) an education campaign aimed at the power companies to let them know of this device.