These "confuser" books might be cheating but there are only so many possible questions on what is for most part an absolutely ancient syllabus, largely unchanged since the last world war.
The books contain about 4x more specimen questions than the exam, and I think that anybody who can work through them and get say 90% right HAS to have an acceptable understanding of the subject.
Most of the stuff is not needed anyway for actual flying. (That will get some people going
)
I don't think Trevor Thom Book 5 is very good, although it is clearly intended for the IMCR. It is very confusing in places and unnecessarily complicates what are IMHO relatively simple subjects. How many pages can (should) be written on how to track an NDB? People write reams but it won't sink in unless (until) the pilot has developed adequate situational awareness.
But I never found a better book when I was doing it. I did find good books on parts e.g. VORs/NDBs (Martin Cass) but they still make a meal out of it.