No, there are no implications for quitting a full-time job after 6 months especially if you are talking about big4 because as mentioned earlier, there are many, many others who have done that.

That said, I don't think 6 months at a big four as a full-timer is useful experience. It is too short to include it in your resume and I'm doubtful you'll get any references/testimonial. You're better off interning at a law firm or getting some other non-accounting/audit experience.