As you've probably guessed, it's about punctuation. The use of each punctuation mark is clearly and simply explained, there are examples of its use and, where helpful, suggestions to avoid misusing them. It seems to me to be comprehensive and accurate. Typographical marks, rather than punctuation marks, are not included.
It's cute; maybe better described as a booklet than a book. The cover has that strokeable finish you sometimes find on nice notebooks.
The book is very short. There are just 36 pages and funny little sketches (illustrating the examples) take up half of each. Those shown are the first and last pages, reproduced with the publisher's permission.
That does make the £10 price tag seem a bit steep, but has the advantage of making it very quick to find the information you want. I have other books which provide the same information, and much more, but they don't make it easy to check if you suddenly have a doubt over whether to write women's or womens'.
The website states the book is for all ages, but especially designed for teenagers and those who feel reading a book is boring. I think it would also be good for those writers who don't want to be told how to write, and/or don't want to get sidetracked whilst in the middle of something. It would be a nice small prize for competitions or other writers's group activities. It's not so good for procrastination though!