It really has to do with the person doing the studying. For me personally, I only read the K&B book, took a few mock tests, and then passed the exam -- all in a span of about a week. I thought it was ridiculously easy. Others however, can spend months (years?) studying, taking every mock exam in existence and reading every book on the market and fail repeatedly.
So --- try and make a determination for yourself as to whether you need to spend more time/money/effort to get the knowledge to pass the exam. You know yourself best, right?