I know what you mean... it would be great to have some sort of evaluation feature to the site, just to make sure you're on track. But I suspect that would be an added expense, and I think the monthly rate for this site is super reasonable.

I approach basically like Razbo is describing, but I do try to make sure I'm not building on poor technique. For instance, I won't let the fact I'm struggling to master a chord stop me from moving ahead and learning a new finger picking style. But if that lesson calls for using that same chord I'm struggling with, then I know its time to focus on getting that chord down pat. I also try to make sure that in the end, I can do the lesson perfectly just so I don't leave any unfinished business. I find it helps to keep a journal, taking notes of what needs improvement so I know what to focus on next practice.