Would advice the authors to have a demo/sample as there are many that claim similar functionality but as a user you want to get a feel this one actually works.
Unless this is one of those “landing page only” startup ideas to see if the idea would work and enough are interested to make the product. In that case I wish them good luck.
Sounds like a terribly hard space to succeed in when we life in an era where you get personal recommendations on sites like HN in minutes and Google already seqrches the entire space on every possible review that is public.
In addition the internet is pushing back on books via companies sharing their experiences via sites backed by OpenSource projects.
Books still have value though, and finding good ones is a nice feature. Your tagging and suggestions really need to be top notch for users to really want to pay for that but if you get it, who knows.
Best of luck!