I think it's useful as a tool for browsing a getting a general gist of what people are into and seeing if your favorites are there, too. As for a tool to maximize one's reading list, certainly not as useful, but I appreciate that it didn't make me feel like I had to create action items on things to read.
OK but there's no clue what they are until you start poking around. It's not something that's useful without some substantial investment of time and exploration. If that's the goal, fine but it's not how I would present a "favorite books" list.
Making 'genres' and classifying things is imprecise and requires experts in subject matter and library science to get it right. The "genre" labels here emerge out of the data itself.