As someone who doesn't have unlimited fast mobile internet in Switzerland, I was practically unable to use this app. The Gruyeres Castle has only one Wi-Fi hotspot that's in the reception area. Everywhere else you have to rely upon cellular.
The app uses old API, so it seems to crash frequently, at which point it loses its mind and starts downloading updates, which never completes at my access speeds.
After a few trips back to the reception, I was able to listen to the guide in a couple of rooms, and even see the augmented reality. Then it crashed once again, and I gave up.