NO products basically help pump the muscle and are sold mainly in proworkout products. From the data I've seen, they will not directly contribute to new muscle gain. But that being said, if I can get a good pump, I'm more likely to focus more on my workout. If I have a wk's worth of good workouts, I'm more likely to grow, than if I were less focused. So maybe in an indiredct way, an NO booster may help with gains.