Sure. But even when you add noise to the described experiment, you get useful data.

That is the point I am making: Experiments of a single person can be useful.

The critics of single person experiments usually come up with examples vastly different than the Theanine experiment described here. With long term experiments which are only conducted once. But the Theanine experiment was looking for a short term effect and can be conducted many times. The hammer experiment I made up would be an extreme example of this type of experiment which leads itself well to be conducted by a single person.

What I am trying to point out is that if you are a skeptic, it would be better to try and find weaknesses in the experiment at hand. Not making up completely different experiments.