I bought this book because it was cheap; a bestiary didn't seem like something Castle Falkenstein needed, and I was not expecting it to be a great enhancement to the gameline. I was wrong. This book does so very much to make Falkenstien's world more strange and magical, and has provided me with a wealth of inspiration. And it manages to do this while maintaining Falkenstein's tradition of having a strong feeling of in-universe authorship, without succumbing to the pitfalls usually associated with that approach (which is to say, Tom Olam's constant asides about how technology is bad and Thomas Edison is a witch). Honestly, this is probably one of my favorite RPG supplements of all time, and I highly reccomend it to anyone who is considering Hosting a game of Castle Falkenstein.
...HOWEVER, there is one significant technological issue that I must mention: On my preferred PDF reader of choice (Foxit), this is the single slowest and laggiest PDF that I have ever had the misfortune to encounter. There is significant lag while scrolling as well as long 'load times' on each individual page. The issues are better when opening the PDF in Microsoft Edge, however, so I am willing to concede that this may be an issue with Foxit and not deduct any stars from this review.