thanks for this free ebook from OP, and i read through all pages to share my minds here.
The book revealed around 100 niche websites that categorized into different niche groups.
Each small niche share a sample url and screencut from semrush.
I think this book can be used to do niche and subniche research, if you have no clue where to start.
However, if you dont know SEO, you might not be able to dig much out of these websites. This is not a guide of how to do SEO,
but if you are experienced on SEO and niche research, this small ebook is surely your handy tool.
thanks