I endorse what liam548 said: the PPL confuser has a small number of mistaken answers (<2%?), but it is very effective at getting you through the exams.
I got my worst exam result in my strongest subject (Nav), possibly because I took it before I discovered the confuser, (though a ruler malfunction didn't help either...)
The IMC confuser is pretty good too, when you get on to that.
If you want to understand the subjects in depth, neither exams nor confuser may be appropriate, but that wasn't your question!