The Pupper Masters, if I'm not mistaken, was Heinlein's first work to be published as a novel, although it first appeared as a magazine serial. This would explain some things - as an earlier work, it isn't as well written as some of his later stuff, and writing for an sf pulp magazine probably necessitated a more rapid, gripping way of writing. The best of Heinlein's sf works are stylistically similar to the this one, but the style does get more refined and skillfully used.
The story itself is so-so, but it's notable for a certain tone of distrust of authority, or at least of the government machinery ('the President is the prisoner of Congress') which anticipate Heinlein's full-flown libertarianism in other works. This was also a rather unusual tack to take in the 50s, when, at the height of Cold War paranoia, people were more inclined to treat their government as asbolute and infallible. The heroine of the novel is only the first of several gorgeous, red-haired, capable and romantically oddly soppy heroines in the course of Heinlein's writing career.
