The pass mark is usually 75%.
The PPL Confuser contains about 4x as many questions as the exam paper, i.e. say 100 instead of 25 so by the time you can do them OK you are virtually guaranteed a good pass in the actual exam. The PPL Confuser is definitely worth getting.
The Trevor Thom books are OK, except book 5 (Instrument Flight) which is rather disjointed and was probably written in bits, by different people.