To answer your question, we have quite a bit of original content and functionality beyond the book lists and transcripts. And based on my experience assembling customized homeschooling curricula for my kids, the book curation in itself is a major value add. If it saves the parent just a few hours of research time, or connects the student with just a few resources beyond what parents could find on their own, it would be worth the cost for many families.
The main differentiator in a homeschooling curriculum is what the student will spend his/her time doing and reading, and optimizing this seems like it would be worth paying for a service rather than relying on free book lists from the internet. That's our hypothesis, anyway.