I know that Campbell's book is recommended by some flight schools in Australia and used as a text book. Flicking through it, it seems very good.
Some years ago I liked Kershner's book and I see that it is kept up to date although aimed at USA instructors. You can peek at a 13 page sample here
https://www.asa2fly.com/The-Flight-I...ver-P3862.aspx
I didn't bother keeping the textbook that I was given when I did my flight instructor rating in the early '90s.
Most new flight instructors that I encounter in Australia have never seen the CASA Flight Instructor Manual. Certainly that is a good thing with regard to stalling and spinning - one day it may be revised.