From what I understand, glucosimine is for joints. Not sure that it would help ITBS.
If you are oging to take it, go for the 'good' stuff. Because it is a suppliment, they only have to prove that it isn't harmful. So the store brand probably isn't going to be the best... My dog was on it for awhile, and since it is a veterinary product, it's regulated by the USDA, not the FDA. So the veterinary product is a much more pure product.
When I was taking it I got it from AmeriScience. My BIL is a doctor and has seen good results both with himself and his clients.