Comparing a book to other books on the cover
I've been looking into fair use law, but I'm not finding an answer to this specific question.
Is it fair use to compare your book to another book on the cover of your book?
I'm working with a client to publish her novel and we've written the tagline: "It's Devil Wears Prada meets James Patterson." I know titles and names aren't protected by copyright, but since it's on the cover, could the author face legal action, since she's using the names and titles of other works to help sell hers?
I know it's common to have these sorts of comparisons in reviews and query letters, but I can't find anything about using it on the cover of a book.
Any help would be appreciated. Thanks