Honestly speaking, something similar to this concept has already been made and used(Check flywheel batteries/generators) and a few companies like Toyota and NASA have already done a fair bit of research and prototyping on it. The only benefit this thing has is the low maintenance cost and longer life. It is touted to replace conventional batteries if the product is successful in functionality.
So, first of all it isn’t a ‘free energy’ concept. There is some form of input energy required to move the flywheel and this is the energy it can store and be put to later use as a ‘generator’ in all likelihood.
Second, if providing continuous input would be a problem, you can think of using it as a generator only, where the input could either be from some existing used energy source(like electricity) or it can be miniaturized, powered by your own motion(walking, cycling or any form of exercise) and used as a small charging device for your smaller electronic devices. That I guess would be the best way to use this device. :D