Hi Igor,
I bought Imperial years ago when it only cost about 60 bucks (not that cheap in those days!) and it really got me hooked on collecting Imperial Lugers in general and Imperial Navy Lugers in particular.
Görtz/Sturgess is a monumental work, it's more up-to-date and contains everything you need to know and even more that you don't need, but it's a textbook and a pretty dry read.
In the end it's your choice
Norm
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