I am taking it next week and I used both the ACCP and High Yield Med Reviews. I thought the ACCP was more complete and up to date. Some of the HYMR is pretty dated. I do like their Q bank, though.
I'll try to remember to advise which one was more helpful when I take it, I was actually hoping for some tips and insights here!
The ACCP material comes with a "workbook" but I bought the book in 2019 because I thought I would take it then and I didn't, then COVID hit. Anyway, I liked the 2019 book better. It was an actual book. This is individual handout chapters you have to download and print. It also comes with lectures and audio you can download and a practice exam. You can use the audio lectures in your car or whatever.
High Yield is lectures (they are shorter and less in depth, but do hit the high points) and a test bank. There's no book (which is one thing I really liked about their BCPS material, but apparently they don't give it now. They have an ebook, but it's hard to use) and no way to download the lectures.