I started viewing the Eterna expecting to find at least a couple major faults. I've been toying with it for a couple days so far, and frankly there isn't much I can say bad about them. The biggest gripe I have is that the cord is sort of stiff and doesn't like to lay over the ear well without snugging up the slider under the chin. That's pretty much the worst thing it does, lol. Frequency response is excellent, digs really low with good visceral capability and the treble is fully capable up to the limits of my hearing (15kHz-16kHz).
It can use a small amount of EQing. A quick run through with pink noise, I ended up putting a wide cut of about 4dB centered around 200Hz between 50Hz-1kHz, added a narrow 3dB bump around 1.4kHz, and shallow 2dB cut across 4kHz to 12kHz. This largely balanced out the presentation.
The sound stage and placement of sounds is excellent. You get a very good sense of pinpoint location and good sense of distance. Depth sounds appropriate, although it's not massive like a few earphones, nor is it overly closed in.
Presentation is clean and quick, perfectly transparent, and with good separation of sounds. Bass is a dominant factor in the sound, not overbearing, but it's deep and authoritative. A 30Hz tone is not a problem. Bass is excellent on this earphone. Midrange and treble is good, clean, well detailed, offering a normal amount of edge/bite and dynamic emphasis. It doesn't quite offer the micro detail of say the CK10 though. The overall presentation is driven by the bass like most of the time, not overshadowed, but driven. Dynamic range is ok. You don't quite get the sense of subtlety nor any real explosiveness that would rip your head off. The range is good and comes across as appropriate but it's more compressed than many of the other high end options. It does make it a little more pleasant with bad recording, but it shows the driver choice is geared a little more for critical listening than rock out at a million dB.
Amping needs are minimal. It doesn't take much to drive them. I do find that because of the amount of bass and the driver choices Fischer made, it is somewhat limited in raw output before you get a tonal change due to compression of the lower frequencies.
Very cool for a $60 earphone. It certainly hangs right up there with the big dogs. It might be slightly limited by (perhaps) budget driver choice, but its implemented very well and just offers a whole lot of good.