I use this book as a help to compensate for my poor memory: I know the term but the exact definition has fled my mind. Matthews book is suitable for this purpose, because the entries are compact and in a few lines give you an overview, which on the other hand means that the entries only give a minimum of information. The compressed form also result in many definitions being explained using other definitions: You can't use this book to pick up linguistics from scratch, some basic knowledge is required, Or you will find yourself turning pages going from one definition to another trying to make out the meaning of what you first looked up (and since the paper seems to be of very poor quality it will not last you long if you have to turn too many pages).
But overall I think the book is worth buying (especially for the student). And since it is written by Matthews you can be almost sure the information in it is correct.