Ah, yes - EVIL. A really evil race and no apologies. Demonically cruel, unfathomably, unhumanly evil. What campaign world doesn't need them?
Seriously, they're a great addition to any world, especially if you want to introduce them as an ancient, forgotten evil race the players stumble on to, as I did. Basically, if you think of way to enter them into the campaign instead of just dropping them in as another monster, they'll be quite memorable.
Regardless, it's more than worth the money; much more detailed than most monster entries in the rulebooks, and you get one color version and a b&w printer-friendly version.