The lack of negative reviews may seem strange, but I genuinely believe that everyone who has written about HR does so in a sincere manner (whether it be positive or negative). I can understand how it seems shady, but with a $17k tuition, a "free" hoodie is not enough to sway a review one way or the other.
That's intuitive but factually incorrect. There's a large body of empirical research that shows that giving away trivial tokens has a significant impact. This is true for everything from charitable donations to sign-ups for services to survey responses. Not to mention ratings for college courses, which are, in the aggregate, more expensive than Hack Reactor.