Well, according to the second law of thermodynamics, a heatpump is a physical impossibility, you get 400% efficiency out of a device where Th is colder than Tc.
There is a confusion here between "efficiency" and "coefficient of performance", which is the metric used to rate a heat pump's output. http://en.wikipedia.org/wiki/Heat_pump
When comparing the performance of heat pumps, it is best to avoid the word "efficiency" which has a very specific thermodynamic definition. The term coefficient of performance is used to describe the ratio of useful heat movement to work input. Most vapor-compression heat pumps utilize electrically powered motors for their work input. However, in most vehicle applications shaft work, via their internal combustion engines, provide the needed work.
When used for heating a building on a mild day, a typical heat pump has a COP of three to four, whereas a typical electric resistance heater has a COP of 1.0. That is, one Joule of electrical energy will cause a resistance heater to produce one joule of useful heat, while under ideal conditions, one Joule of electrical energy can cause a heat pump to move much more than one joule of heat from a cooler place to a warmer place. Sometimes this is inappropriately expressed as an efficiency value greater than 100%, as in the statement, "XYZ brand heat pumps operate at up to 400% efficiency!" This is not quite accurate, since the work does not make heat, but instead moves existing heat "upstream".
A heat pump moves heat by mechanical means, so inevitably the conversion of electrical energy into useful work is not 100% efficient.
Anyway, I don't think these guys are claiming 100%+ "efficiency", cos that would be a perpetual motion machine.
I think the tech they might be using is this: