What model Vokera is it? I have the Hi Comfort control, it works fine.
Not the most intuitive to use or prettiest room control but there's no need to go to it with the Hi Comfort app.
The predecessor, the BeSMART was excellent but let down by the servers in China which were incredibly unreliable, Hi Comfort uses Amazon servers and I've had it for a year on test with no issues (I also work for the company).
If your brother goes Hi Comfort use the OpenTherm option, it'll squeeze a few more percentage points of efficiency out of the boiler.