Completed IREX this morning with a 90% result.... right about what I expected.

I used the BT book and online practice questions, plus some coaching by a commercial airline pilot. While the book was very good, and I would say sufficient for a solid pass, having access to someone who explained various bits and pieces and answered my questions was a huge help. If you're going to attempt IREX, I thoroughly recommend tapping into relevant knowledge at your flight school (find a tutor or coach).

With the CASA exams, lots and lots of practice beforehand is enormously helpful, and I can recommend the BT online practice exams. If you're scoring well in these exams, you're ready for the real thing and you can expect to do well!