I got a one year. Wonder why they offered different terms to different customers?
Full-disclaimer, I've never heard electrostats. But my guess is, "speed". Attack and decay that are much better than dynamics, and help create a better sense of realism. Planars and electros are awesome because they are so damn 'flat' in response, it seems to come down mainly to upper-midrange and treble response in separating the good from the great.
My impression is that the HE-500 and HE-6 are still the benchmark for what hifiman wants to be able to achieve, so I expect a more "natural" response to become a descriptor of the HE-400i.
Once the electrostat is releases, I gotta get it.
Preferably along with a reasonably priced HFM electro amp :]
To be clear, the new models are Planars - Not Electrostats. But I am sure they will be worth a listen.
I just sold my HE-400's in anticipation of buying these. Stupid decision? Maybe. But I'm pretty excited about the HE-400i. I loved the HE-400 but it was definitely one of the least comfortable headphones I've owned and the earcups were just a tad too small to be circumaural for me, as others have mentioned.
I'm wondering how many driver revisions I should wait for after they go on sale before I pull the trigger though...