Clough42 gets free 3D printers from manufacturers sometimes to review, and every once in a while he tears the product a new one. And every once in a while the company actually uses said negative feedback to improve the product
Far lower than that. Most EEGs at the scalp are in the 10-100 µV range.
https://www.audiodesign.co.uk/index.html
I'm guessing he expected to see Mark fail to repair it, and instead talk about how amazing and advanced his product is.