Those Osprey books are really cool. I got one Jagdwaffe: Luftwaffe fighter pilots 1939-45. It covers their training and equipment. It totally reworked the way we, as a squadron, trained our pilots to pass their "wings".
I also got JG27 Afrika and it gives great insight into details you just cant find anywhere else.
Great books, I highly recommend them. They a quite cheap aswell for the content.