I signed up to the HSK6 course; I have almost finished week 1. The videos are 15 minutes long, but still it takes me like half a day or more to study the material to the point where it's not incredibly difficult. (I write everything down, search for example sentences, and input the new words into Skritter for practice [the words I don't know; I also add a few of my own choosing].)
I also find it hard to believe that it will cover all of the HSK6: I don't think this is the intention of the course. [And I observed that some of the new vocabulary does not belong to the HSK, and hence this post.]
At the same time, does it really matter that it's incomplete? Regardless of anything else I'm making progress. And if I don't study the difficult material, then it will remain difficult until I study it at a later date.