Seems to be a Swiss app, and they say they're open source (didn't see a link to the sources in a quick look), here's their twitter feed through nitter, they seem to be ok. Here are the details of the shop
Berlin has a new Bitcoin merchant!
The Subway branch Chausseestraße 22, 10115 Berlin-Mitte now accepts Bitcoin payments via the Lightning network.
Here's the sign on the Subway store:
https://i.imgur.com/9qY5W20.jpg
Here's the link to the wallet app in English
Seems to be a Swiss app, and they say they're open source (didn't see a link to the sources in a quick look), here's their twitter feed through nitter, they seem to be ok. Here are the details of the shop