Seems to work. What do you imagine is the main use case?
The website also have a microphone and a speaker test. They have some interesting use cases, mentioned on the website.
P.S. The UI is awesome. Is it written with flutter? Also, I'd love to be able to better control the frequency slider in microphone test. Either via logarithmic scale, or via "+" & "-" buttons, or via text field to set a frequency manually.