The faction decks seem to have pretty much everything you need to build an army in them, and they're only half the price. Paying the extra for the book could be useful though, but I like being able to sort through the cards, and think about what a possible army could look like.
Rules-wise, I don't think the Faction Book adds much more than the faction deck, except the "Tier lists", which are simply themed lists, which aren't really necessary. If I were you, I'd grab an battle group boxed set of an army you like, and think about going from there.
It's all in the name.
Looking for a club in Brisbane, Australia
? Come and enjoy a game and a beer at our friendly club in a pub, Sunday nights from 6:30. All brisbanites welcome, don't wait, check out our Club Page on Facebook
for details or to organize a game. We play all sorts of board and war games, so hit us up if you're interested.
Update:From the 25th of May 2014 we'll be Meeting at The Junction pub in Annerley, opposite Ace Comics and Games
Still playing 40k, Warmachine and board games of all sorts!