I like this book which is clearly written by a practitioner rather than an armchair occultist.
Exorcism is specialised branch of the work and this book does not try to be 'all things to all men'.
I would not recommend this book for the beginner in magickal practice, as it assumes that you have a fair amount of foundation work in place already. For the more experienced, this would be suitable as a serious introduction to a complex study and practice. In particular, there are some excellent tips on general hygiene, in the magickal sense, on karma and/or fate and the realities of seriously following the path of the adept.
If you complete all the work thoroughly you'll probably be ready to write a grimoire yourself.
If you enjoyed Harry Potter and the Philosopher's Stone you'll love this book! I have to say that it is very readable and moderately entertaining. However, most of the claims are not only highly suspect, but also come with absolutely no supportive evidence. Indeed, the author does not at any stage explain how she arrives at her often preposterous conclusions, aside from intimating that she comes from a long line of priests and priestesses.
The author claims that it is possible to be `possessed' by everything from demons through to fairies (which apparently come out of vortexes), angels and evens gods and goddesses. She also divines the type of possessing entity through using a Tarot deck. Oh, and angels have absolutely no sense of humour and show signs of asberger syndrome! It's all a bit `airy-fairy' and `new-agey' ... and dangerous. `Dark' entities do exist but, if you're in trouble, following suggestions in this book could be like throwing petrol on a fire.
If you have a practical interest in magic then I'd recommend to study all three volumes of the Magical Knowledge series first - then move on to the Exorcist's Handbook. The money invested on the four books is worth a library spent on traditional 'grimoire' or GD type of books on ritual magic. If, however, your interest is mainly historical or theoretical and you aim to just peak behind the veil of what is really going on during an Exorcism - then go on and take a look. There is no better book out there than this.