content: Down side, really none. But its very over simplified in this video. It makes it sounds like its around the corner, when people have been saying this for 50 years and its still 50 years out. (We first demonstrated fission in 1952 to give you an idea)  If you want a simple example its easy to make the fission happen, but hard to control something as hot as the sun and feed it. For a generator like this to work it'd have to harness something as hot as the sun, while feeding the reaction, and not letting it get out of control. One example of this not being used for good would be Thermonuclear weapons like an H bomb. Which use this energy to give off a lot on energy at once. ( On the plus side, its pretty fucking rad tho) See https://en.wikipedia.org/wiki/Thermonuclear_weapon