What are the benefits of a diabetic taking this vanadyl sulfate supplement?

In the health food store, the salesman recommended that I take vanadyl sulfate. I am a diabetic, what are the benefits of taking this supplement? Are there any side effects?
I checked the National Institute of Health’s Office of Dietary Supplements, several drug references and cannot find any information about vanadyl sulfate. Beware of persons without degrees or a state license in nutrition who offer nutritional advice. This can be illegal in some states that license persons who can give nutritional advice or call themselves a dietitian or a nutritionist.