Just taking it wont by itself help you gain muscle mass. Preloading does cause you to store more of it in your muscles. It is used in that brief interval when you're running out of oxygen and you're going anaerobic, where it lets you extend your effort a bit more. If that's the way you're taking advantage of it, it should help.

It does have an additional effect; it causes your muscles to retain a bit more water, giving the illusion of more muscle mass. When you stop taking it, though, the extra bulk goes away.