I used it as well as his practice exam. I found both to be very useful. I took and passed the exam in April 2018 (one and done) and IMHO this was my 2nd best reference. I, personally, thought Graffeo was a little more helpful, but these are excellent. The biggest thing holding the technical reference guide back is that it did not have an index. On a timed exam, with 6-minute average problem time, every second counts. It sucks when you KNOW the problem can be solved by info in this book, but with no index it takes you 2 minutes to find it instead of 10 seconds. Graffeo has a quick to use index. I really wish Justin would create an index. It would help push this from an 8 or 9 to a solid 10. That said, I would still HIGHLY RECOMMEND it. The price to value ratio is off the charts. There is no better reference for even close to the price of this. It trumped most other references I paid $100+ for in terms of applicability. Buy it, and his practice exams. You wont regret it. As a side note, I printed it at work and brought the paper to Office Depot and had it nicely spiral bound and covered for only $3!