I have tested my M92 and I do not see any bad pixels.
Maybe that the problem has only certain batch of production... Mine was from 'Ebook Reader Discounter'.
Anyway, even if I would detect the defective pixel I wouldn't send it for replacement, because I do not see anything wrong while reading.
To my opinion, the issue is not of big importance. It is BW, so the defective pixel is not too much visible in real use (as opposed to coloured pixel on LCD). Also the pixel size is much smaller on e-ink than on LCD. It also decrease practical visibility of defect. And also we are used that print on normal paper is not always perfect and the paper itself is not always uniformly white.
And also, while searching for defective pixels, I found, that my display is after month of using covered by dust. And the dust looks like many defective pixels...
I should clean it time from time.
But I agree, that there should not be any defective pixels in a reader costing +-400 EUR.