Pros: Extreme extension both ways; supreme detail; perfect bass quality
Cons: Highly dependent on proper amplifier/source; darkish sound; long time from order to arrival; large
SE-5 is a true marvel of engineering, one of a few headphones/IEMs I can say brought a new level of detail and presentation to music and is truly high-fidelity, that is directly comparable to live performance given a high quality recording.
Important caveat: many amplifiers and sources (even many dedicated headphone amps) cannot drive SE-5 correctly - very low output impedance is required.
As a workaround, an impedance adapter can be used to reduce the impact of this on sound.
When improperly driven, they sound dull and dark due to exaggerated cut around 5-8kHz, unevenness above and lowpass. They're relatively dark in the highest registers anyway, which is the reason for 0.5 mark off the sound; but they're no darker than most dynamic driver IEMs.
(No, you don't really need a Benchmark DAC1 for them - FiiO E7 will do.)
Also, I had to wait about 4 months for them to be made, then had to get a refit, taking another month.
Of course the price is very high even for custom IEM standards, however you do get unparralelled quality for it, especially in lower registers.