I found the N Sornying PPL Confuser to be excellent at preparing for the exams AFTER reading the Thom books. I haven't seen the Stephens book so cannot comment on it.
N Sornying also does the IMC Confuser so make sure you get the right one, with a black cover (for PPL) as opposed to the IMC one with a green cover.
If you are just starting out then you won't be needing THOM book 5 for a while either as it is for IMC training.
Agree with FFF that CAP 413 is better than the Thom book.