FWWC Readings

[Partizanka]

One of the reasons that brought me to start wargaming, long time ago; was to play through the battles I have read about in books.
I always try to match games and books that portray the battles at the same level.

Recently I was hooked up by the FWWC titles Serbia and East Prussia, but I am lacking good reads about them.

I was thinking to buy:

For Serbia '14: Serbia and the Balkan Front, 1914 by James Lyon

For East Prussia '14: Collision of Empires: The War on the Eastern Front in 1914 by Prit Buttar

Are they good choices, do they have the same scale of the games?
Any other suggestion?

Serbia and the Balkan Front, 1914 by James Lyon looked good and I ordered it after sampling the first chapter. I supplemented  Collision of Empires: The War on the Eastern Front in 1914 by Prit Buttar  with Tannenberg, Clash of Empires by Dennis Showalter. I'm curious if anyone read August 1914, by Aleksandr Solzhenitsyn and would recommend it?