I was supposed to write a book for them. Even though they refer to people as experts, table of contents and page count is given up front and is hardly negotiable, so I decided to not proceed. Instead I reviewed the book written by someone else and I'm confident they are not a publisher worth working with. Even though I tried my best as a reviewer the outcome was at best mediocre. Language review is done after the book is done, so it's hard to focus on the content. Half of my comments were ignored because they would cause major rewrites (as a reviewer I was contacted after initial drafts of multiple chapters were completed). And the only payment is a copy of reviewed book.
I don't think these books are worth even $5.