It would prevent lockdowns because contact tracing would be fast and it would keep numbers of people that you infect low.

Unfortunately, if you do not have symptoms, you can still propagate the virus. There is a difference between pre-symptomatic and asymptomatic, but you can't know which one you are if you don't have any symptoms.

Asymptomatic people are people that will never have symptoms, and pre-symptomatic are people that will have symptoms, but don't at the moment.

If you're pre-symptomatic, you can spread the virus. Pre-symptomatic people could be responsible at around 40-45% of all cases iirc.

About the potential of abuse, like I said in other posts, is really low and not really viable (technically and economically) compared to using technologies that already exist.

I'm not sure what you mean by "staying power"? But unlike the flu, Covid-19 doesn't have any treatments. And the death rate of the flu is around 0.1%, For covid 19, it's hard to tell right now as it changes a lot from country to country, depending on testing, etc. But it's about 1% from what we know.