From the bits of research I've read, and from my personal experience, I don't believe that NO products do much for actual muscle growth, but I can tell you that they do give me a better pump and when I have a better pump, I'm more likely to feel better in the gym. When I feel good, I train hard and hard training leads to muscle gains. So indirectly, I believe that NO products can help with gains. 

As for PWO's that contain stims, that's a whole other topic. I think that the industry is getting carried away with the amount of stims they put into these products. Stims aren't going to be productive for gaining new muscle. If I'm feeling low energy, I'll consider using a PWO, but it seems like a lot of people are hooked on training with a PWO. These products weren't around when I was 15 yrs old, but I get the feeling that some of our youth don't know what it's like to train without them.