The class I'm teaching in February will only have the basic mBot to keep the costs down for the kids (they take the robot home at the end of the class), which is why I'm trying to avoid requiring additional purchases for the class. I'll be pointing out other Makeblock products that would make some of the programming in mBlock easier as we go.
Right now I'm writing a short "book" to support the class which I'll self-publish afterwards (I want to see how the materials work in class first) and then I'll be moving on to create additional tutorials, etc. in mBlock and Arduino as part of the ongoing classes I'll be teaching. I'll be publishing those as well.
With regard to the line follower, I can get three states, but for my purposes I was only testing to see if both line following sensors are over the line. I hadn't thought about the serial delay, but you're likely spot on with that and it explains some of the other behavior I've seen with sensor readings.