xxJIYOxx I think it is a useful tool if you would like to make some bulk purchases and like to check which stores have the cheapest price in store order.
I don't think that sorting would be that useful here. We group offers per game, so if 3 stores have the same price for the same game, we display this game only once with "random" offer from these 3 stores. If we sort results by store then, you still may miss some offers, because we randomly picked offer from the other store.
I think that "only current lowest" filter in combination with store filter would be more useful here - you could easily find other interesting offers from particular store and use more practical sorting (like rating, price or discount).