I have attended several of MPX's seminars, both for audit and rules updates. The first one I went to I was baffled by all of the acronyms they used. RDFI?, ODFI?, PPD?, NOC?, what is that? The second seminar I went to I asked them to please explain these meanings or to provide a quick reference help sheet to the beginners. The gal putting on the training was so nice, she began explaining as she went along what all of these things meant. So if someone gets ahead on you, just ask them to slow down or expand upon what it was they just said.
Having said that, and now being a seasoned ACH auditor, I would recommend purchasing the ACH Audit workbook. I purchase it every year. Why? Because it will always address any rule changes and I don't have to create and modify an internal workprogram each year. It is a life saver!