Some girls I knew in college wanted me to be a "test subject" for it. The herbal compound definately worked, which they found quite amusing. However, I agree that these herbal substances are far more dangerous and less effective than actual regulated drugs. "Natural" doesn't mean safe or healthy. There are "natural" roots, mushrooms, herbs that can kill an elephant.
I'd go with Viagra over Levitra. If I wanted the long-term thing, I'd use Cialis.