I said basically the same thing: it would be nice to be able to grade yourself (A, B, C, D, F) after each chapter, at least then you could remember how well you felt you picked up the lesson and could go back later to redo the lower grades later. I personally get to a point where I feel comfortable that I've the general idea down, that I can play it decently (at least a few times without messing up), and then I move on. If I get to a point that is too difficult then I go back and redo a couple of lessons, then try the difficult lesson again, then rinse and repeat.
Right now I'm stuck on the faster transitions between chords (80-120 bpm) and learning the annoying B min, F min and G min (I stink at any chord that requires you to lay down a finger over multiple strings), so i'm just doing those mixed in with random older lessons so my hand doesn't fall off. Hopefully barre chords will be my salvation.