I’ve been using the Mudita Kompakt for over a year now in Canada - I have the North American version of the phone. This year I went travelling to Europe for the first time with it. Here’s what I found:
-Boarding passes worked fine on the phone - I downloaded pdfs and added to the stock e-reader app, also downloaded photos of QR codes and could open in the gallery app
-Got an e-sim in Poland no problem - texting and calling worked fine, data was kinda slow but I think this was the service provider rather than the phone. Good enough for internet browser / email, too slow for hotspotting and streaming video.
-Relied a lot on Whatsapp to stay in touch with people in Canada, glad to have this
-Sideloaded yahoo mail app - doesn’t work great on Mudita but good enough for viewing and replying to emails
-Took photos with a separate camera and I have a separate music player
-Navigating was not an issue for me because I had family leading me around mostly. If I was alone with the Kompakt, though, I could see this being a challenge. I would then come prepared with a paper map and look up transit routes in advance, etc. Or maybe a small tablet to hotspot google maps? A few times we were without our family guides, my partner hotspotted off me and we used google maps. Or he would say “let’s get lost.”
-No need for translator cos I speak the language - I would sideload a translator app if I were travelling elsewhere
-Used sideloaded browser to occasionally look up a restaurant or bar to check out and once to look up the local taxi company and call a cab
-I brought my laptop as a backup but honestly barely used it. My kid had an ipad for the plane and train rides, and I think next time I’ll rely on that as a backup device
All in all, it’s great to travel without a smartphone. 
