I would assume the key reason anybody is using this app is to find iut how to get their same "weekly shop" for the best.

Here is how I think that should be accomplished.

First off a user should be able to create a list of what they want to buy - this would be awesome if they could take a photo of a receipt and maybe identify a few items manually where there are issues. If not then at the very least a user should be able to create a groceries list from generic products or via a products at a single supermarket - this becomes the baseline like "here is what I have just bought this week in ASDA".

Then the app should be able to offer some suggestions - I imagine a user would select how many different ahops they are prepared to go to and narrow down a list of what shops they have nearby (like now) The app would then work out the cheapest the user can get their shopping within the criteria they set. So if they chose to only go to one supermarket you would tell them where they should go from the supermalrets they selected to get th best value. If the user had said they are happy to visit up to 3 shops then the app should work out the best lists for each shop within that criteria.