It's been set up by someone who is both an author and an IT professional, and it shows in the design of the site - its functionality - and in its practicality: it really serves a useful function.
The impulse behind the site was to create a space where readers could nominate the kinds of books they were interested in, then be told when promotions or events relating to their chosen fields were approaching. In that way they would learn in advance when a particular book was about to be promoted - probably at a cheaper price - or when a favoured author was organising an event of some kind, whether it was a personal appearance or a blog tour, for example. This means also that authors can identify when they're promoting a book beyond the Amazon eco-system, simply by describing it in their events calendar. These events and promotions are then listed on the Home page of Readers in the Know in a kind of newsfeed so that readers are constantly advised on upcoming events.
Another key features of the site is that authors can identify all the markets that their books appear in on Amazon, and the formats in which the books are published. This means that no matter what country a reader happens to be in, they're informed of the correct price and directed to the correct site to purchase it. Most book promotion sites link you to the Amazon US site, so that if you happen to live elsewhere in the world you have to do some scrabbling around both to find the book and then check out its price. Readers in the Know does all that for you.
All in all, this is one of the most professional book promotion sites I've seen. It's properly designed, has bags of functionality for both readers and writers, and contains lots of information to help readers make up their minds whether to purchase or not. There is even a series of comprehensive videos explaining how the site works, both for authors and readers. It's been well thought-out from beginning to end. Very good job.
The Home page is here: Readers in the Know.
PS If you're an author or publisher signing up to the site, you can use the following code when setting up to earn £10 of advertisement credits: GXBECWSB.