Hello.
First Aid was my major source during the studying process, and I found it very helpful. I think it has all that you need to pass that exam successfully: all topics that you need to know are covered very well in a very compact way, it has many pictures, charts, funny and easy to remember mnemonics, facts. Also I liked that it has a lot of free space, so you can write down your own notes and the paper of this book is marker resistant, even to strongest markers.
While reading it I have found few mistakes, but I still think that the book is great.
If you don’t understand something, or it looks like you want to know more so that to understand some material better - you can refer to the topics in the subject-based textbooks or internet.
Alongside with First Aid, I was also using Dental Decks, Dental Boards Mastery App on iPhone, Released ASDA Exams, Netters Atlas, and also I had separate subject books for each of the sections of the exam. I was referring to these textbooks whenever I felt that I wanted to know more details or to get better understanding 🙂
I would definitely recommend this book as a benchmark in your NBDE preparation.