I am not certified to the ASQ CBA, but my experience with several of their other certifications has been that if your study material (e.g. QCI primer) covers the scope of the
Body of Knowledge you shouldn't feel that you are missing much. Primers
will not contain the text of standards or reference documents (such as from the FDA or GHTF) so you may want to supplement your study materials with those freely available sources. Keep in mind that the BoK also calls out what
level of cognition the exam is expecting you to have for each area of the BoK.
As with many other ASQ certifications, it appears that the CBA leans heavily on Auditing (45 questions) and QMS (50) and general Quality Tools (15) with only 25 questions focused on the specific technical area. This doesn't mean you can fail most of the technical questions and be certified, I only point out which areas will contain the most questions. If you have other ASQ certifications certain areas will be familiar to you.
Sidebar: The ASQ question banks are created by volunteers who are given some basic amount of training in how to write questions at the required level of cognition, with the additional requirement (at least at the time of my most recent participation in one of the more technical areas) that "Primers" could not be used as the source of knowledge for any given question; all questions had to have one or more primary sources. The question bank contents are subjected to some round-robin evaluation, so I can say that 'your mileage may vary' when it comes to the wording of the questions as well as if they hit the appropriate level of cognition. It has been my experience that less experience question-bank writers lean too heavily on the remember/knowledge level, this bias occasionally shows up in the certification exams. Another peculiarity that I have seen is that the forced reliance on non-survey primary sources if that occasionally (usually 1 question per exam) there will be a question worded in a very specific way that is unique to one (primary source) author's area of specific expertise.