I remember this ad. I read a different book from the same publisher back in the days and was completely offended by having an ad in a book I just bought. The upside was that it could be removed without removing any text from the book.
That's not so bad
It was on two pages such that you could tear it out. The first page was almost empty with a small teaser and on the other page you had the ad text and a small logo.
I found it very weird and it is awful because it tears you out of the story. You lose the flow.