The extension is primarily aimed at the USA marketplace, and is for use in conjunction with other shipping carriers, usually those create live rates such as UPS, FedEx, USPS. The general rule is that if you have a shipping carrier and want to override in certain scenarios then Shipping Override will help you do this.
Shipping Override is not a shipping carrier, it does not produce shipping rates on it's own. If you need such functionality then look at the MatrixRate suite of extensions on the website.
Head over to our landing page for Shipping Override today !