I sat PoF in Jan this year, and passed with 94%.
I must say, there wasn't much Bristol. Maybe around 60-70% of the exam. A lot of people did fail this one, and I heard the average mark was 70%.
Bristol isn't the answer for subjects like PoF, Gen Nav, Instruments, and Met. If you learn the principles of the subject, you can apply them to any question.
Bristol is a much better tool for subjects like Law, and HPL, and Comms, and possibly Radio Nav.