I actually use courses C, D, & F with my middle school elective class. I start them out in C because they haven't really had much exposure to coding. Once they are finished with that, they move on, but they skip the Ramp Up lessons and I have them start later in the course. Many of them have found it to be quite challenging and all but one stayed engaged (there's always going to be one! )
I think it totally depends on how much time you have. I see my students 2-3 days a week for a semester. If I saw them less, the Express course might have been better. Hope this helps!