It's possible to use cryptographic techniques to retain anonymity. That doesn't mean implementors will, but they could. AFAIK many of the companies rolling out solutions already have our location anyway and they are just offering "in house" solutions using data they already have. Combine that with the voluntary aspect and I'm fine with at least the principle.

As for efficacy. I think people's expectations are too high. Ready to shoot down something because it is not perfect. People can take the information given with a pinch of salt and apply their own knowledge to it. You were in a grocery store for 5 minutes and someone else was there diagnosed. You took every precaution of wearing mask, washing hands and handling items purchased - probably not going to give a damn. You spent the morning with someone, a friend of a friend perhaps, who now has it and may have let your guard down - quarantine yourself. Ditto for when people start going back to work in offices. Saves a lot of effort trying to let people know and probably not bothering. I have a hard enough time reaching my friends these days so any help trying to contact essential strangers is welcome IMO.

Those who choose to ignore it, or have over dependency will have a less than perfect experience. As in life YMMV.

It seems to me this is useless unless privacy is sacrificed. I have heard something being done by anonymizing data, but how would that even work if you can't identify anyone? What would be the point? Tracing relies upon identifying individuals. This essentially makes it very similar to the idea of chipping everyone, which seems to scare a lot of people, and rightly so.

I keep thinking of the film Minority Report.