Apparently they sent the device in themselves. I suppose they were expecting "cup the balls" sponsored content treatment rather than an unbiased video.
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.