I have taken ZMA for a while, by Primaforce. I'd definitely recommend it. Yes, it won't put much on you in the way of muscle, however, it definitely gives a deeper sleep. The dreams that you have on it are unreal. That deeper sleep induces better recovery, which in turn can lead to better gains. Personally, I rate it, and that's a lot considering that I think that the majority of supplements just constitute money down the drain.