I think my Four Stars are misleading. It is worth Five, if you account for the price and market of the book.
"Line by Line : How to Improve Your Own Writing" provides solid information on editing your own writing and therefore, improving your writing for professionals needs, but it doesn't meet my needs as a communications professional. Writers, in general, will find this a worthy tome, but as a professional copy editing my coworkers and clients I think you'll find this a bit limited in scope.
For the price, "Line by Line : How to Improve Your Own Writing" can't be beat, but I recommend spending a few more dollars on a more thorough text. Check out, instead, an Associated Press Manual of Style and far more meatier text, like "Copy Editing For Professionals" by Rooney and Witte. You'll pay many times more the price, but in the long haul, you'll be glad you did.
I recommend "Line by Line : How to Improve Your Own Writing" but with reservations.