Hi banmanj,
Thanks for the feedback, we definitely take it into consideration. With that being said, we're already working on a feature like the one you're talking about. At the moment it's only available on song tutorials, but what it does is it automatically scrolls the tabs/notation as you practice the song, so you can play along with the instructor.
At the moment, the feature is only available on the song section.
In order to slow lessons, you can click the gear icon and select the speed. You can slow a video down to half its speed, or up to double its speed.
Again, thanks for the feedback!
Best,
Billy