This book has about 50 pages of dictionary, followed by word lists by category (such as the family, days, months, numbers, colors, foods, and animals, among others), and finally a page of "vocabulary tips," which are things like "English -ous is often Spanish -oso."
One major disadvantage of this book is that the dictionary section is Spanish-English and there is no English-Spanish section. Obviously, with only a little over a thousand words, the book is not meant to be an exhaustive dictionary, and it does not really function as one. I was surprised at how useful I found one part of the book- the list of foods (Spanish-English, like the dictionary section). There were many words on this list that I did not know but felt I should, such as "almond" and "celery."
I went through the dictionary section and found that each page (with about 22 words) had an average of 4 words I didn't know. (To give background on my Spanish knowledge, I have taken 4 years of high school Spanish, plus a lot of reading and studying in my spare time). I happily highlighted those words and began studying them, since they are, as the title claims, very useful. I think that this book might be most helpful for someone who has taken around 2 years of high school Spanish, as that person would know far fewer of the words. On the other hand, it might be an overwhelming amount to memorize, so maybe not.
Here is an example entry taken from the book (I think this falls under fair use...):
"arrojar to throw Se prohibe arrojar objetos por la ventanilla. It is forbidden to throw things out of the window." At times the entry will also specify that the word is used in a certain country or region, which is very helpful considering the variation in the language in different Spanish-speaking countries.
All in all, a useful little book, and a good resource for learning Spanish. Its scope is small, but it achieves what it aims for very well.