How do they know it's a bad product if they didn't bother to test it under the conditions it was designed for? It was a prototype, not a final product. In the original video, Linus is surprised (and maybe a bit upset) that the other guy didn't grab the right card or even notice that he didn't get the right card.
And to the point of the comment you replied to: it doesn't matter what the cost of the cooler was. If it was the best of the best then it was worth showing that. LTT does not seem to have a consistent viewpoint of "practicality". Even if we ignore that, saying "this product isn't worth the cost" is very different than the "useless" comment they ended up with.
The whole situation is what I like to refer to as "fractally wrong". No matter the perspective, how close or far away, it's always wrong.
Yes he was, he commented on it in the original video, which the GN video included.
My bad, I should not have quoted a word that they didn't use directly. But still, his final conclusion, as included in the GN video, is that nobody should buy it, and not just because of cost.