I would say "ineffective" for several major reasons.
[...]
This looks (as advertised) very like the NHS app in the UK (as advertised, again). Whether because a common development (either way), shared ideas or just parallel evolutionary pressures.
I never actually used it (like I never use my bluetooth, or GPS, or NFC, or anything that is useful for one or other of the methodologies in use - not even a QR scanner!), which might or might not make me unable to properly (and unhypocritically) comment further on it. My excuse is that, aside from passing people in supermarket aisles, which would not have registered as long enough record a potential future proximity warning, I was not actually ever going to be in the presence of anybody
except my 'bubble', in which I was the sole owner of any variety of "smartphone" anyway. More luddite precautions and (potential) response were far more failsafe. And it meant I waa never tempted to leap into any illegal moshpits to risk both my own health and my fragile device.
The big thing that happened over here was the "Pingdemic". People with positive tests for Covid (who needed to isolate themselves) created a whole lot more people with the App telling them they were close contacts (and therefore, at that time, also had to isolate themselves). Complaints abounded that the bluetooth ranging mechanism worked through shared walls between terrace houses, so even without actual meaningful contact (brick- or stone-cored walls, no risk of aerosol dispersal through those!) a family on a sofa in one living room could end up recorded as being within feet of the future-positively-testing neigbours as they sit on their own sofa.
(And then, while the precautionary contactee-isolation waited for theirvown home-test to be negative, their tentatively-reopened place of work/education had to adapt to their absence, etc, etc.)
That unsubtle ranging issue aside, and my own non-participation, I was annoyed that to combat the Pingdemic they turned down the sensitivity. I reasoned that if the phones weren't more likely to register than a real infection was to take the opportunity to hop, then it was going to miss too many cases. We already had disruption, and better just a little too much more than necessary than even very slightly less. (The rush to end the first, second and third lockdowns undoubtedly helped to set up the
need to have the second and third ones, then leaving us where we are now which
looks more like normal, but probably more to do with the vaccine availability (for those that take it up) than any safe-contact communal mentality.