Musk used the "Rapid antigen test from BD," which is a different test from a different company.

This has been debunked.

He likely was using it incorrectly. The president also used it incorrectly; Abbott called him out for it.

Abbott's tests only work if you have symptoms, it's as simple as that.

If you're asymptomatic, the results will be 100% unreliable.

Wasn't the biggest concern of this whole pandemic asymptomatic spread?

The Abbott ID Now is not authorized for use to detect asymptomatic spread. The machine was coming to market even before COVID and was developed to be an accurate rapid test for doctors offices and other appropriate places for diseases such as influenza. https://www.medtechdive.com/news/abbott-on-defense-id-now-co...

The White House used it for that purpose anyway, it seems to have been moderately effective for a while but they ended up having 3 super spreading events because of relying exclusively on the ID Now tests (used against directions) and without masking, social distancing, or ventilation/outdoors events.