It’s a 3d printed mount and 3d printed ear with a calibrated linear mic attached with approximately the same ear volume. It does the job for me, and I’m not keen on spending hundreds to thousands more for a iec711 clone or whatever b&k everybody using these days. I may change out the ear one day for a silicon cast of my own ear, since that can be done pretty cheap.

Just got mine in from the 11.11 sale. A week later than my bud despite in the same city, cursed bundling different orders I spose.

I have the he-x4, which is what these are supposedly, and it seems to be the case. Primary difference beside the headband is the pads. The he-x4 used a microfelt/velour hybrid whereas the 400se v1 uses a mesh hybrid, and that’s where the primary audio differences come from. I measured both on my crude measurement rig.
https://imgur.com/a/UjZmDx6