In the meantime, I'm thinking of how I might hack it with what I have now by just using URLs attached to text like "Help me! I don't understand!" to out-of-book auxiliary resources to provide another perspective on some of the slipperiest topics (like "growth rate" vis-a-vis derivatives).
I really would like to know where people stumble with these activities... and then fix it. So that feature would be really helpful. Or if someone wants to copy this and change it themselves, go for it! I put this up on Geogebra because it is a fully open platform.
Which brings me to another reason for going with Geogebra: your point.
Geogebra books are a nice balance of free hosting, wide distribution, and a reasonably friendly UX format. That said, it's hardly perfect. But it offers me what I think is my best chance to fail fast, get feedback, and make changes with the approach to teaching calculus that I present in this book. But I want to fully acknowledge your point regarding UX. I absolutely agree. The "Geogebra Book" format has its limitations and introduced new assumptions along the way that make it harder for users. If nothing else, it's A BOOK. There is an inherent "one-way-ness" to it. I don't see that being as much of an issue as you, but I agree some of it needs to be broken down. How else will revisions make it into the book? That's the whole point of it being open.
As a sidenote: I also want to point out that I have tested these activities as best I can in a variety of LMSs and in a variety of classrooms from Ivy League students gunning for top marks to adult learners who "can't do math" and gave up on Calculus 20 years ago, but due to some reason or another now need to know it. This book is sort of the "least common denominator" of all these testings, and is itself a testing.
So... you're right! Thanks. Want to work together to test it more?
I've already changed it just from reading these comments, and I'd be really interested in continued revisions!