From what John and I learned at an HVAC show in Atlanta in the 80s, the technology, usually in a heat pump application because of the climate, originated in Japan because of space and construction considerations.
The thing that worries me about them is, as Pete was telling us last year, the incredibly poor filter at the intake of the inside units, not that the situation is specific to these, just made worse by the lack of space in which to put an additional filter.