Straight from their website:
What are the differences between the two products, "Stainless Works" vs. "Stainless Power"?
Because we have designed both products to have very similar acceptance standards, there are few visual differences. The main differences will be in the header flanges, which are slightly different. For instance, the "Stainless Power" LS1 header flanges contain four oval holes, while our "Stainless Works" header flanges contain all round holes. We continue to provide a full lifetime warranty for our "Stainless Works" header products, but only a two year warranty for the "Stainless Power" products. We carefully control all aspects of our internally produced "Stainless Works" products, allowing us to offer a full lifetime warranty for these products, something we cannot effectively do for subcontracted "Stainless Power" products. "