Does not work when I switch from WiFi to cellular connection (At&t LTE in NYC) on my Lumia 920... Just keep showing "network communication issues" messagebox, no matter what (I've tried closing it, re-installing it, etc.). Kind of worthless in its current form :-/
Edit: managed to get it to work - I ran the app while still connected to WiFi, then without closing the app completely I turned WiFi off and switched back to the app, that allowed me to measure my cellular network speed... As soon as I close the app completely then try to run it again while on cellular network (disconnected from WiFi) - it starts to display this error message again... WTF Ookla, test your apps properly before releasing them in half-finished way!