[throwaway55421]

Until it auto updates.

If it even matches the source as is. Play Store and App Store are non reproducible.

[simion314]

Do you pay cash when you go to restaurants or shopping? If you pay electronically then why do you trust the payment system? (it is not open source,reproducible and for sure your purchases contain much more data then what you imply the QR code scanner collects)

[lmm]

Many Germans refuse to use anything but cash for that very reason, so this isn't a very strong argument.

[emteycz]

Yes. And meal tickets for most people here - so cash equivalent.

[throwaway55421]

Yes.

[sc11]

It's on f-droid with reproducible builds.

Obviously there's a risk that the person scanning the QR code does shady things with it but it's rather unlikely the app itself will. It would be caught really quickly.