Receiving auditing:
I had some Book 1, but that's about it. My recollection is that it was a fairly idle activity. It seemed to lack any contentual motivation. A great deal of attention was paid to superficial phenomena ("indicators") but otherwise it seemed empty to me. Auditing commands were either too easy to satisfy or were impossibly hard and invited confabulation. It was all talk, remembering or trying to remember various stuff and attending to reactions with no real thinking involved. Perfect for the lazy person who is content to sit there and introspect in a wholly uncritical fashion. Whilst a stranger fatuously "acks" at you!
Auditing others:
I audited others on Book 1 and Grades 0 and 1. Toward the end I was told I was getting good at it. This might have been true or it might have been flattery to keep me encouraged. At any rate, as an auditor I increasingly got the sense that no matter what the needle did and the C/S wrote and no matter what the PC's reactions were in session, I could not possibly be helping the person in any meaningful way. This was evident from the constitution of the "tech", written in plain language, and the intended result, which delivered no benefit -- only elicited some superficial "indicator" from the PC.
In hindsight I'd say this. It's far far easier to explain why a few people are tricked into thinking auditing "works" than it is to account for any actual improvement in the face of apparent counterexamples. This is how I'd argue it now, but even at the time I had a strong feeling that the burden of proof was on the upholders of the "Tech" to explain how and why it allegedly worked, given my own direct experience that my sessions for others were doing nothing worthwhile at all.