It's a good thing but, is one of those natural supplements that really has to be taken with caution. In my opinion it's right up there with Ephedra/drine. You have to start out with a very small dose and see how you react. If you have ANY family history of heart problems, high blood pressure, stroke, anything like that, I would stay away from the stuff.
You'd be much better off with something like Arginine, viagra, or anything else that wont mess with your heart rate.