Covid antibodies used in these instant tests often attach themselves to other SARS viruses, which are present in millions of people.  This can cause an alarming number of false positives, which led to an incident in Manchester, Vermont where 61 out of 65 people who tested positive didn't actually have Coronavirus.

Distributing these tests is better than nothing, but just barely.  A better use of resources would be to build labs and hire personnel that can perform more reliable PCR testing on a scale that would give us test results in time for contact tracing to be useful, but Trump will never do that.  He is content to let us keep dying by the thousands until the vaccine is universally available.