Kirkland/Costco doesn't manufacture or blend oil. They buy blended bulk oil from those who do and package it in their own proprietary containers. Costco brands, IMO, have always had my respect as far as quality. (they aren't perfect) 10 quarts of synthetic oil for $2.50/quart is a good price provided the oil meets the specifications (in your owners manual) required. Any quality oil, synthetic of not, will have the specifications it meets written on the container. (API, ISO, ACEA, etc.) You can always pay more, if you want. It is your responsibility to confirm that the oil you purchase meets/excedes the requirements of your specific application. In short, you have to decide if good, . . . . . is good enough.
Chum lee