The first two risks are only unchanged for a demonstration that was not announced to japan, and IMO a demonstration of a nuclear bomb without telling Japan to observe it would not have been effective.

After the bombing of Hiroshima, Suzuki stated to the press that Japan would not surrender, which suggests to me that bombing the middle of nowhere as a demonstration would probably not have persuaded the Japanese government to surrender. Why would a non military demonstration have been more impactful than bombing a city?