I do have personal experience, at least in following the advice of that blog post. After reading it, I bought the Dell S2722DZ which is 27" 2560x1440 for 108PPI. It's a decent monitor and I haven't had any issues with scaling, i.e. the "native resolution" of the monitor works with the output of the OS and there's no need to waste CPU/RAM on scaling the pixels. The text isn't as crisp as on a Retina, but it's way better than the previous cheapo monitor I had.

Not sure my opinion counts for much though, since I didn't try any monitor in "the red zone" and thus have nothing to compare it to.

This Dell model does have a 1px column of dead (?) pixels that appears sometimes, but if I squeeze it then it goes away. I think it's due to some loose wire in the paneling... but it's not too big of a deal, and regardless, it's unrelated to PPI or scaling or whatever.