Can I use BookSirens if my book is in Kindle Unlimited / KDP Select?
We have promoted over a thousand books enrolled in KDP Select / KU over the last three years and haven't received any complaints so far. That being said, we cannot predict the future and we recommend using review services like BookSirens at your own risk if your book is enrolled in KDP Select / KU. Since KDP Select / KU is an Amazon specific program, we also suggest contacting Amazon support to clarify their guidelines.
We take some extra precautions while promoting books which are enrolled in KU to better adhere to Amazon's guidelines. We ensure your book does NOT appear in the public domain on BookSirens. For example, your BookSirens book page will not appear in search engines like Google, Yahoo, etc... Furthermore, even if someone clicks on your book cover, they would need to register and login before they can access your book page.
To indicate that your book is enrolled in KU, follow these steps.
Books on Preorder
Even though you may have enrolled in KDP Select for your preorder title, note that the KDP Select / KU term begins after your book is released. You can therefore safely promote your ARC on BookSirens until the publication date and stop the promotion thereafter.
You can enroll your pre-order book in KDP Select, and the KDP Select term will begin on the book's release date. - Source