I personally have not tried them (yet), but from my experiences, take what you read with a grain of salt until you can try them out for yourself. Either my tolerance for "bad sound" is quite high, or it's that people are capable of exaggerating to the point of hyperbole.

To be fair, you do also have to take into account the asking price for what's being offered; and it's the same with any other headphone. Take for example the Focal Elegia and Hifiman HE6se v2, both were largely deemed as "not worth it" at their respective MSRP's, and for a variety of reasons. However, now that Adorama are pricing them at or below the $400 mark, suddenly, more and more people can now tolerate the faults (i.e. sound quality, build quality, comfort, etc.), which by the way have not changed - only the prices have.

So, for an MSRP of $2399, it's understandable that the expectations for the HD820 didn't quite meet the mark, but for used prices of ~$1000 (or less for some lucky few), can they now become acceptable? It's all just a matter of perspective. :)