Whiff - I had a look as I was curious. It's a trial run by the University of Cambridge in collaboration with other universities and NHS. www.safer.phpc.cam.ac.uk/
It seems like a proper medical trial. I agree that the only reliable ECG is one done by proper medical staff, but for paroxysmal AF, the chances of having an episode while being monitored are quite low.
In my case I would get AF, (detected initially by taking my own pulse) around once a month. The device I was recommended allowed me to confirm that I was in AF and send the result to my GP. He referred me to a cardiologist who was happy to accept the results of the device. Of course I was referred for other tests - proper ECG (but not when in AF), Echo cardiogram, 24 hour BP monitor. But the actual diagnosis was because of the small device and I was put on the appropriate medication.
The main reason for early diagnosis of AF, which this trial is about, is that it leads to a greatly increased risk of stroke and many people have no symptoms.