I wouldn't mind hearing your criticisms of the interface. I use a fork of this book largely for the UI (not intentionally, that's just how things worked out). I am not a GUI-person, I just use Bootstrap as defensively as possible. So far, I haven't had any complaints about the affordances, but then most students don't complain unless things have gone terribly wrong. If you have specific things you can point to, it'd be helpful for my own purposes.