I've been a lurker, but my understanding from most people's posts is that the KBB isn't as challenging as a test-prep book ought to be to yield comparable or better results on the actual DAT. Most people use the KBB as an overview to understand field-specific weaknesses prior to plodding along to focus on their areas of improvement. That being said, I have certainly seen people who do well with just the KBB (i.e. AA minimum of 20-22).