Note to people unfamiliar with David Weber series. This book takes places in the universe of the Honor Harrington series (which started with On Basilisk Station). One of the stories, A Whiff of Grapeshot, might give more background into the series than one might like until after Honor Among Enemies, and the last part of the book gives general background into the universe, including history, politics and technology. For these reasons, the overall value of this book for non-fans of the series is rather low.
For the *fans* of the series, on the other hand, there are three reasons to buy this book.
First, the first tale, A Beautiful Friendship, tells the story of the first contact between human and treecats, a six-legged arboreal telepath sentient being alien being with some very feline features. Insights into treecat's culture and abilities, the story of the first adoption, and why do 'cats like celery so much, all of that you'll find here. It also shows that some of Honor's ancestors could give her a good run for her money. :-)
Second, the third tale, tell us of some events that happen at the beginning of In Enemy hands, on the side of The People's Republic of Haven, which are only refered to in that book, never described. Insight into Haven's leadership minds.
Third, the last section of the book, is a pretty deep background on the physics of space travel in HH universe, how the universe was colonized, history, geography and politics of the Kingdom of Manticore, history and some politics of the Solarian League and the People's Republic of Haven and comments on the military capabilities of Peeps and Manties at the beginning of the conflict. It covers nothing of what happens after the beginning of the series, nothing about treecats and nothing about Silesian Confederacy or the Andermani Empire. Moreover, all the really important notes are already in the series. Still, for those who just MUST know everything there is to know about the series, it has interesting details.
David Drake's story is a disppointment, though. While the story has a few remarks to link it to HH universe, you would just have to change a few names and one would NEVER find any relation between this story and that universe. I suppose the story might be good, but this is just not Honor Harrington universe.