I got through with the bob tait book and an AIP in 3 days. I had little choice as I had a window while I was down from Kununurra and had to start the MECIR training.
Bob Tait got me an 80% pass first go. I was pretty happy with it considering the time I put in.
Having said that, my knowledge was very lacking and I didn't understand operational IFR. It took the rating and a couple of years and renewals to get very comfortable with operating under the IFR.
Bob Tait will get you through, but it won't teach you how to be an IFR Pilot. The only thing that will do that, will be lots of revision of the documents with suitable mentors (not know it all Slingair Pilots for instance :P) Most of that knowledge you pick up in your first multi crew job flying with very experienced Pilots