I also used kahn academy for similar reason and I think their quality changes depending on the subjects. For me the real value came from their exercises. You get a problem, you don't know the answer, you open all the hints, after a couple of exercises of doing that you see the pattern, and then you have learned that specific thing. When I got stuck was when I watched the videos. It also helps the watch them at 1.5 and 2x respectively, depending on your need.