The problem of offline QR code payments have been solved in a much low-tech way... https://cdn3.i-scmp.com/sites/default/files/styles/980x551/p...

I see main utility when you need per-item/per-transaction billing.

Instead of having to print static-per item tags, or redirect users to a website with online checkout, you can have that thing to generate individual codes for each piece of merchandise.