I am fairly comfortable answering this for you... You are correct in that the front sight is on the barrel. This is called a "sight tracker"... The theory behind it is that when you fire the pistol the slide is moving, and so is the front sight. With the sight tracker, the sight is on the barrel... and stable/in place, your follow up shot will be quicker as you are never waiting on the pistol to cycle and the slide to return to "aim again". Makes perfect sense in theory, and is more practical for competition type shooting where speed is critical. I personally do not think that I am qualified to say that I would notice the difference on those follow up shots.
Master USPSA shooters love these fine blasters, so I assume the theory is true in the right shooters hands...