Nothing is too heavy for my >15kg touring bike . At least the weight difference is minimal as the average hub dynamo adds ~300g to the wheel, and one Magnic Light is ~150g. According to the other thread, the maker claims the power output is 1W @30 (!) km/h. This is no surprise considering the size and the fact it is basically a bottle dynamo with (eddy current) magnetic coupling instead of mechanical.
But having the option to easily move it from bike to bike is great, I do hope they soon make a scaled up version and ditch the light in favor of USB.