I remember taking one of these, but I always erred on the side of caution because of this specific paragraph:
During the initial setup, you adjust your headphones to a loud yet comfortable volume, preview what the test will sound like, and take a practice round. You can also specify what type of earbuds you’re using for the test.
The loud yet comfortable volume could mean many potential things, and realistically, every person has a different set of headphones, the same way they have a different type of hearing loss, if they perceive they have one. The practice rounds are also a little odd if the test isn’t randomized in terms of the tones generated.
I think what I’m trying to say is there are many variables to take into consideration, i.e. volume, headphones/earphones, perceived vs actual hearing loss, other settings on the phone/computer the user may not know about, and even whether or not they’re using a wireless bluetooth enabled headset, or a wired headset, if the headset is wired into a pre-amp, and so on.