Oh nice, thank you. Will check it out later!

What I suspect though: They mainly show current discounts. The REWE API exposes those as a separate list for each market. There's around 3.5k markets and each can set their own discounts and has their own product catalogue with their own pricing.

So it would be 3.5k API calls to fetch all offers for all markets. Which is doable.

But fetching all products takes like 100 calls per market. It's quite a bit of data. And I think most supermarket don't publish their catalogue at all since they don't have delivery options.

2.8 rating in Play Store sounds bad