a "add to virtual cart" button is added to every product page. Click on the browser extension to see virtual cart. Click aggregate to get the list of merchants with the greatest number of cards from your selection. Secondarily sorted by lowest total price.
once you click "add to cart" click the refresh button or reopen the extension to re-aggregate the remaining subset.
The 3 prices listed are: minimum price, minimum price out of sellers on this list, and the actual price from that seller.
