I had an interesting conversation a few days ago with a lad who had been thinking about buying a Haibike with the Yamaha motor fitted. He said that he had decided against the idea when he spotted that only the low end Haibikes were fitted with the motor, and questioned why if the motors were so great, that Haibike didn't fit them to high end bikes, over the Bosch motor.
I like the look of the Yamaha unit, and I would imagine that it will be pretty much the most reliable and possibly bullet proof unit available, but the question that the lad raised, was something that I hadn't even noticed or considered before. Good observation on his part though.