TL;DR: It's actually technically a crap pattern (even forgetting that it's not 16c, and not the eInk palette), but it works surprisingly well in practice on eInk, as can be gleaned from Jon's picture.
I mean, it's definitely worse than doing it The Right Way, but it's not so awful that I want to tear my eyes off, far from it. And it's definitely a win vs. not doing anything (for unprocessed content, which is 99.99% of content on Kobo)

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On newer devices, what's done looks even better (and isn't as aggressive towards perfect content, which is a double win in my book). The clincher being that it's free on Mk. 7 (in terms of CPU cycles).