It's not very often that readers get the opportunity to engage with you as an author, but this widget opens up a dialogue between the two. For example, you could add just the one feedback widget towards the end of the book, or add one after every chapter. This can be a great way to find out which parts of your book stand out and which parts need more work.
The widget works by opening up a feedback form inside the book, and you can ask for the reader's email address if you want to reply directly. You don't need to publish your e-mail address as Bookry handles everything for you and all replies can be viewed on your Book's settings page on Bookry.