[MENTION=6563]Azzy[/MENTION] has a great point, and it has given me an idea: I'm going to share the primary reason why I, a long-time D&D player with a full collection of Forgotten Realms supplments, am purchasing this book (besides that my players might like to use any mechanical options found in it).
It could serve as an outline for how to efficiently present Mystara setting information to my current players, who have no more knowledge of that setting than can be found by me constantly mentioning random cool esoteric factoids from it and playing the arcade games Tower of Doom and Shadow Over Mystara, that are currently in their first campaigns set in Mystara (and are, luckily, playing characters that are as unaware of basic info about the world because they have only just arrived their from an old home-brew world I am abandoning and Oerth).
I've looked at other campaign setting products and books and found them to be lacking as such an outline because they are far to lengthy (busy lives and all means not much time to read, and I don't like feeling like I am assigning "homework" for a game) or designed in intentionally disjointed ways because other books were to be coming along to fill in, so this book might be the one to help me, since it is both relatively brief and also released in the current "we aren't pumping out tons of books" era.