I majored in economics, graduated with a 2.5 GPA, no finance or accounting background, passed L1 with 4 months of study. Ironically, I failed the econ section.
In other words, people that walk around saying how easy a test was that they took in the past oftentimes forget the stress and difficulty that they actually experienced in the moment.
I read Derivatives by Thomas Miller as a prep for L2. I think it was helpful as background knowledge and actually learned a lot reading a textbook presented in a different manner than CFAI.
For me, I read Schweser CFA prep 99.5% of the time, then the CFA issued books 0.5% (rounded up) of the time. One year it was 100% Schweser - the CFA books remained in the sealed box and are still there blocking a mouse hole.
Any other finance / economics / statistic book, I either burnt or frieghted to a storage locker in Saudi Arabia so that I couldn’t waste any time reading them.
At one stage I thought about going to a CFA exam prep class held by some guru. Then I realised, the only thing of any value he could tell me was the stuff in the CFA books…and I had the books…so I cancelled the prep class and went to my room to read the CFA books.
It turns out the CFA Institute is a boring bunch of the people - they said they would only test me on stuff in the CFA books and they didn’t lie. Very boring. For L3, I even included information I read from a Damordaran book (during my MBA) - it turns out they took marks OFF because I wasted their time with uncessary reading.