I did not go through the entire course, but went through about half of it before selling it, declaring it 'rubbish'.
There's really no special secret that he reveals. Basically, the tapes (at least the first two I listened to) consist of him talking in a quiet voice and then playing a note, and then saying something like 'Now, listen to the quality of that note - that's an E flat. It has a specific timbre that is unique to E flat'.
This was over 10 years ago, but I doubt it's been updated much more than the core method which is 'listen to various notes and try to distinguish them by their quality'.