I just got my OV21 this weekend. I only have a couple hours on them so far, but first impression is very good. This headphone is buckets of fun. The strong, energetic bass and sugary-sweet highs remind me of my Teaks, which is by a wide measure my favorite headphone in my collection. It's not quite on the same level as the Teaks, but it also is cheaper, so you still get what you pay for, at least. And especially considering I got these for $280 on their Black Friday/Cyber Monday sale, that's some extraordinary value. At the full price of $400, I'd have to advise one to save up just a little bit more and stretch for the Teaks instead, but if you can get these at $280 like I did, they're a slam dunk and a half, extremely easy to recommend. That price puts them in Meze 99 territory and I'd have these over the 99 any day of the week, no hesitation.
Something to say about fitment, though. I do have a mighty big noggin. To give you an idea, in the past I've had people recommend me things on the basis that they also think they have a big head and a thing fits them, only to find that their recommendation doesn't fit my apparently even bigger head. That being the case, the OV21 just barely fits me. Really gotta pull down on the cups and stuff my ears in there. Once the headphone's on, things are mostly fine. But there is not even a millimeter to spare for me. So, if you're like me and your head is on the especially big side of big, you might have problems.