Cicero's prose style can be difficult for students breaking away from the simplicity of De Bello Gallico and Pharr's heavily padded Aeneid into reading Latin with greater fluency. Whiteley does an excellent job with the notes, although his dictionary appendix is too much of a crutch. Overly particularized definitions for some words are highlighted while more common meanings are omitted. It may not matter however, if the student is only interested in Latin as a hobby and not seeking full mastery.
I would have made a number of different choices in punctuating the text given its intermediate level, but nothing too major.
De Amicitia is not necessarily Cicero's easiest prose, but by no means his most difficult. It seems however, to avoid grammatical monotony, thus I find it a good text for acquainting intermediate students with a variety of possible constructions. The language of De Amicitia is not as highly nuanced as much of Cicero's other work, and in his preface, Cicero openly explains his stylistic intent. The subject matter is thought provoking, and the sentiments memorable, although perhaps a bit repetitive. I partake of the general consensus that Cicero was neither a first rate nor original philosopher, but that he was a very Roman one, and he had a unique talent for interpreting, comparing, and modernizing older ideas.
I sense that Whiteley had very clearly in mind toward what kind of student he wanted to gear this book, and has produced a fine reader in which there are no significant flaws.