Although this is a big book, bigger than Ulysses itself, I found it invaluable. I read through each chapter of Ulysses then read again studying it with the help of this book and a few other resources, then read the chapter again without aids.
The information I got from this encyclopaedia made the whole experience of reading Ulysses richer. I also found that some subjects alluded to took me down rabbit holes and I learnt so much. Without this book I would have missed out on wonderful worlds below Ulysses. So I would say this book is fantastic.