Overall I really like what you've done here Jon!
The mock-up looks nice. I like the "show/hide" text, personally. I
suspect
others will want it removed.
I think it's better removed but what are other people's thoughts?
They provide us nothing but trouble. Let's get rid of them. We can tweak the icon in case the function is not cear.
Looking at your prototype in a desktop browser, it's /very/ difficult to know that you can click on the section headers to expand them. While I assumed I could click the section headers to expand them, it took me Tomasz pointing out the arrow to me to notice its existence. I think this is because I was looking at the prototype on a 23" screen - so the arrows are WAYYYYYYYYYY on the other side of the screen while my eyes were drawn to the header text. Similarly, I think having the header text look just like... header text adds to the ambiguity of its expandability.