I had a blotchy screen on two PW1s, both with very pink corners which tied in with a squeaky/creaky noise when the corners were just lightly held - made me think there'd be trouble down the line. Third was lovely and my mum is greatly enjoying it now.
PW2, the first was a tad blotchy - muddy centre to the screen, pinkish edge. Not that strong, but noticeable.
The replacement and the one I bought for my husband (Christmas) are both really great. Totally even screen, light sepia, no issues at all. Absolutely my favourite device. At one point I had three PW2s side by side and both my parents and husband could see that the second two were better than the first, bought a couple of months earlier.
But the timing could have been coincidental, and I absolutely agree that the only thing that matters is normal usage. Its not meant to be a torch (although it does come in handy if you need to find something in the middle of the night and don't want to wake dogs or partner
)