If you can get clusters of people to use it, say everyone in a big office building, it's a lot easier to hit that 20-60% number than in the population as a whol

If you can get clusters of people to use it, say everyone in a big office building, it's a lot easier to hit that 20-60% number than in the population as a whole. IMO these apps will be most useful as a tool to assist manual contact tracing teams at first.