Not only that but the fact that by the method they are following, they will never know what the effects are. That's really what makes it pseudo-science.
They have an apparatus, but nothing else of the scientific method.
The results of a trial are judged in some purely subjective terms.
It's pseudoscience if it's presented as "scientific fact"; science is the process by which such facts are established. Otherwise you're talking about a hypothesis.
Sigh did you read TFA? It's not "just" a matter of establishing effects - article goes into why it's not that straightforward ... as another commenter said TDCS is like using a sledge-hammer to tune a piano. We know that TDCS does "something" but all the hypotheses are "two tailed" which basically means all you can say is there is an effect - not whether it's a good one or bad one. The pseudoscience is claiming these hypotheses are certain.
The article was about people using tdcs for durations and at levels of current that haven't been tested, measured, and documented, and then claiming that it has a known, beneficial effect, while implying that there are no negative side-effects.
When scientists study these effects, they study them over groups of people. For some individuals, it hurts where it should help. For others, they get a larger-than-average boost. At the same time, research seems to suggest that some abilities are increased while others decrease, for a given protocol.
It's not pseudoscience that a lot of people are trying a new, untested thing. It's pseudoscience if they claim benefits based on subjective perception or claim that the same protocol will help everyone, without documenting objective, replicable proof.
They have an apparatus, but nothing else of the scientific method.
The results of a trial are judged in some purely subjective terms.