As the other commenter said, there's a split in people who learn well with mindmaps and others like me who prefer lists.
The startup I worked on: Mindwarp Pavillion in Dundee got licensing rights to stacks of textbooks. They created loads of mindmaps based on study books and sold access to students for a few bucks a month.
Even (better?) the mindmaps were a quiz where the student had to answer the next node. There were studies showing that using this method they retained a lot more information.
I was told that the whole mindmap concept was protected somehow (patent?) which they paid a license fee to use. They also got the endorsement of its creator.
£30m valuation when the local authority invested. They lasted a year then died, leaving my last invoice unpaid.
They failed because: - Students didn't pay - They could do it on pen and paper for free, while they're learning - The product wasn't driven by a real customer need: 12 months of dev on super-whizzy software without getting a MVP in students hands