I think the parts of the test that involve physical reactions will have problems with individual differences. When it asked about which eye was open after being told to close one, in my case the choice was determined by the fact that my right eye is weak, and I always concentrate through my left. I’m sure my physical problems swamped whatever neurological clue they’d have gotten without it. But if they controlled for it, maybe with a checkbox like “vision problems”, it might be possible to remove the bias.