The Hammer's design, which is essentially a traditional clubhead with its face turned upside-down, is a fairly comfortable driver on shots coming off the center of the face. The club is also extremely light, which some players might prefer.
While the Hammer has comfortable sweet-spot impact, its big claim of adding 50 yards to the average tee-shot seems overinflated--there simply is not a tremendous amount of performance to back it up. Under normal conditions, the club has the tendency to produce sprayed shots and rattles the hands on mis-hits. It is also extremely light, which, for some players, can impede the comfort and control of a properly mechanized golf swing.
While Jack Hamm can hit the ball a ton off the tee, his success came before the invention of this novelty club, which is a mere prop in a pitchman's bag of tricks.