I've studied several of those courses. Higher physics and stuff. Believe me, if I can anybody can. I actually flunked out of high school, didn't successfully (sort of but not without trouble) go to college until mid life.
The great thing about them is that they provide visuals (videos, slides, etc.) You can rewind to your heart's content. And so what if you don't understand ALL of it, you will always get some of it. As long as it's a subject you are really interested in, I say go for it.
Plus it's kind of fun to tell people you are taking science classes from MIT or Harvard or wherever. There's some really great stuff there.