This "book" is really just a story, written up and published in book form to give subscribers to Isaac Asimov’s Science Fiction Magazine something nobody else had. Fortunately, I rather enjoy the story—but "Cal" itself is more easily found as a part of Gold. On the one hand, one might prefer to read it there, since it’s more accessible—but on the other, given the general low quality of Gold, maybe one would prefer to read it here.