I don't think they are worthless as such. You certainly can't compare black levels and contrast, different cameras, environments, screens etc have too much impact, but you can get
some measure of overall resolution and colour balance. It isn't perfect but you can get the idea from the 'AE700 (after flicker tweaks) pics' thread, where screenshots of the same 'Gladiator' frame from 5 generations of Panny AE projectors are lined up side by side.
My tuppence worth, Rob.
Actually I just looked at that AE700 thread again and the actual AE700 screenshot is either a poor screenshot or a badly set up PJ, so 'operator error', is another big factor. Oh well, I'll shut up then.

And Comers screenshots
do look good.
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