I can't evaluate the price-performance ratio because I received the eBook for free.
I find it very well structured, a beginner gets a lot of info for the start without having to go too deep right away. I would recommend it especially if you are not quite sure to buy an aquarium.
A small tip:
With the sizes in liters you have always "ziger" attached to the numbers, that reads strange to me.
E.g. 80 ziger - if you speak the number, the zig is already included, with the ending you read then eighty-ziger 😊
But this is only a small thing and no 3 sensation.
The book itself I find as said very successful for beginners.