Coby Pennington Yes, it adds several things to the series and is referenced in Lux as well. I found the kindle/audiobook combo for less than $2.
Raederle Phoenix It's only two chapters. I enjoyed it and I'm glad to have it, but it is a tiny fraction of a book for a full book price.
Smartalec I honestly thought that is was a great book and worth the buy. It takes place right before Firefight and I honestly loved it more then the previous book.
Kitty Don't bother buying it. I got if for half price (Bookseller privilage) and I still feel a bit ripped off. Almost half the book is a preview for Firefight. Read it, but read it for free.