I like the book as a historical reference more than a practical reference. The author takes care to caveat that the spells contained within the book were gathered from multiple religions/countries/timeframes, so most of the recipes call for items that would be very difficult to get. That stated, it is a fascinating book if you want to see some interesting and historical spell craft and ingredients.
Here’s an interesting example:
Insomnia Lice Spell:
Many dream and sleep spells are romantic, but not all. A medieval spell that allegedly encourages sleep relies upon an infestation of lice, which might perhaps explain the insomnia in the first place… 1. Obtain a louse from the insomniac’s head. 2. Induce it to crawl into a bone with a hole. 3. Plug up the hole. 4. Hang the imprisoned bug around the patient’s neck.
I think it is really cool that the author collected spells from such diverse sources, but looking at the lice spell, it does sound like more of a curiosity and perhaps historical read rather than a working spellbook. That being said, there’s nothing wrong at all with reading for curiosity’s sake!