You may use the Big Five, and tests such as the NEO PI-R , in conjunction with any personality theory you chose. And, you will find the theory enriched as the result of being rooted in a commonly accepted vocabulary. I've heard that the Big Five emphasizes the negative, that there are desirable and undesirable qualities that it measures. No scores on the Big Five-based tests may be construed as bad, negative, or undesirable. Any given placement on a Big Five dimension could in fact be undesirable in a particular situation.
Skepticism is good for dealmakers, but beware against bringing it home.
No Big Five trait is undesirable unless something occurs to render it rigid. So, Big Five tests include the full range of normal personality traits, and there are not wrong scores. There can be less than optimal fits between an individual's traits and the demands of their job, family, career, etc. Our clients accept this full range of feedback appreciatively. They like the fact that the feedback is comprehensive, accurate, but not judgemental.