Sound good, workmanship OK, Material quality has room for improvement.

The Hifiman HE400i is the successor to HE400 but probably sound a distinct signature.
As the owner of a closed electrodynamic headphone I had ordered the HE400i for a friendly permanent loan of a Audeze LCD2 because me the magnetostatic principle convinced.
Sonically the 400i could inspire me; an airy sound with relatively precise stage, but quite compact airs.
In the deep bass range is lacking something in the overlying bass he is so tuned to enjoy listening made me to work without too bloated. The mids and highs were tailored pleasant, the centers IMO neutral, more gently in the high frequencies, not prone to sibilance. Sharp Bläsersätze be reproduced in sufficient detail, without the need to make a face when you hear even louder.
A long-term suitable coordination which should arrive pretty good. Who, of course, calls for a super-linear behavior of a KH, should, if necessary, intensive listening before buying sample.

Comfort I call good or very good; on the metal band pegs can adjust the KH very nice; the contact pressure is IMO a good choice for 'normal' heads. Anyone who dares may vary selfsame determined by some bending work.
The weight is also unusual for a pleasingly low magnetostats.
The upholstered sitting pleasant. The cable has unfortunately become a bit short (and why as a 3.6er connector is off and does not open up to me, it will probably hardly anyone want to sit with an open magnetostats in the subway, but no matter; an adapter's case) since but can also provide relief.

As far as the positive.
As a negative to the KH, I feel the following points:
Materials: In addition to the metal bracket is at the hospital on solid materials all cheap-looking plastic. About the material itself can however be argued at 500, - I expect that the plastic either stable and high-quality acts, or the components of eg aluminum (Example: handset forks) exist.
-Continue smelled both headphones (I had to order 2 copies, see below) for 3 days very unpleasant to solvents.
Not this easy new Platikgeruch but the "let's set up on a cardboard cheap Dinosaurer figures from the Far East and smell off" odor.
Processing / Delivery: The pads were wrong, the leatherette threw wrinkles by an unclean seam; (?) that's OK with a 100, - KH, in this price range I can not rate as a positive or neutral that.
If the KH was a part of the packaging, who was not with the other KH easy here.
- (Long-term) quality:
Here I can only guess, but the first one of the KH panel was much quieter than the other and said goodbye to one hour after the initial start-up completely; dead.
The second KH ran flawlessly; yet with me a taste remains. The fact that the Panel of the first KH plays quietly, would at least have noticed during the final inspection.
I have therefore, unfortunately, because sound he liked very much, sent the second KH because of the negative points back.
The HE400i is priced too high for me for the overall concept. If either the build quality is rising, or the price goes down, I'm the next Hifiman determines.
As with any evaluation, these are my personal experiences and impressions; this need not be aligned with the experiences of other buyers of HE400i itself.