This book is primarily for dogs aggressive on leash, same dogs off leash are fine with most, if not all, other dogs. It is only one of 28 catagories of aggression or combination thereof. The benefit to getting this booklet is that 1) you can determine if this is really the problem before you invest in a lot of more expensive books that deal with all manner of aggression. AND 2) You should be working with a trainer on ANY kind of aggression issue. This booklet will help you to know what type of methods are likely to be effective and you will have something to refer to as you are working with the trainer - I would not work with anyone who is not familiar and endorses at least some of McConnell's positive training recommendations.
Her booklets in general cover more information with more pages than you will find in a single chapter of a lot of training or dog problem books. This gives you 59 pages dealing with just one very common, very specific issue! You would get far less for a lot higher price if you brought a book on a more general behavior topic.
If you found the booklet useful, great! If you didn't, be glad you didn't spend more for it, quit yer bitchin and donate it to a rescue group who can use it - it's tax deductable