I bought this so that I could use my Apple headset with a Zoom H6 audio recorder. And it works with a few caveats. I noticed that some of the reviews indicated that it doesn't work with one headset or another, but I'm wondering if those people are aware that condenser microphones require power, be it from a battery compartment that is part of the microphone, or via phantom power or plug in power from the connected device.In the case of the Apple headset, power normally comes from an iDevice via plug in power. In my case, the Zoom H6 can provide plug-in power. This would be a requirement with any cable or adapter. In any case, it works - I can hear sound from the Zoom via the headset and I can also hear my own voice from the headset mic.It may be worth mentioning that this particular cable is a little bit shorter than ideal for the Zoom H6, since the headphone jack is near the bottom of the left side and the mic input is at the upper right, on the X/Y capsule. It reaches, but one has to either run the cable under the recorder, or over the top of it. I attached a photo so you can see what I mean. That's not really a knock against this adapter, unless one intends to use it for exactly the same purpose, and even then, it is workable.As for quality, when the headset is the only thing connected to the H6, that audio quality is quite good. Much better than one might expect after hearing the same headset used with for a phone call from an iPhone. It is as good as some dedicated lav/lapel mics that I have. There is no audible hum, although Apple's mic does have some self-noise, again, similar to some sub $100 lavaliere mics. I believe that one could reasonably use a similar setup for any number of applications and that 99 percent of listeners would think it sounded great.With that said, there is some cross-talk/bleed between the headset and the microphone. If I max out both the mic gain and the headphone volume on the Zoom H6, it actually causes feedback. Keeping in mind that there is a lot of gain going on when I do that. I can hear my own breath quite loudly, so the levels are way beyond anything "normal".Other reviewers have stated that this adapter causes bleed-through with their headset, but I'm not sure that it's fair to blame the adapter because I have used this same headset with the Rode Rec app on my iPhone (and thus, no adapters), and it is possible to cause feedback with that setup as well. So I would conclude that most, if not all of the cross-talk/bleed-though/feedback with this particular headset happens within the headset itself. I would expect differing results with other headsets.And then the shielding issue that some have mentioned. If I connect my digital piano to the H6 at the same time as the headset, I then hear some hum. It's not a lot of hum, but it's there. If I handle the TRRS jack on the adapter cable, it then hums much louder. It's not clear to me exactly what is taking place, but I can only assume that the piano connection exposes the recorder to the AC lines in some way, although, to be clear, there is zero hum when the adapter/headset combination is not connected. For example, if I connect the piano and my iPhone at the same time, that does not cause any hum at all. And other self-powered microphones plugged directly into the H6 also cause no hum.I have a working theory that it has something to do with the CTIA standard itself, because contrary to good engineering practice, that standard puts the mic line on the shell of the connector, which by all logic, is where the shield should be. The only way that one could effectively shield a CTIA connectors would be to use a secondary shield around the entire connector body, which is something that I have not yet seen done. Interestingly, the competing OMTP standard does, in fact, make the shell ground, but Apple has traditionally gone out of their way to buck any and all industry standards, so it's not too surprising that they didn't adopt OMTP. One can only wonder why others followed.If I'm right, then all CTIA-based microphones are going to be prone to hum, which would be no fault of this adapter. One could argue that MillSO could have come up with a way to provide shielding, but at the same time, it's not hard to imagine that they would just go with the standard, even though it may have a tragic flaw. Apple has since abandoned their own standard in favor of Lightning, yet another proprietary standard, and most recently, now that the world has purchased untold millions of dollar worth of Lightning adapters, they appear to be moving toward USB-C, which is bound to be the first time that Apple has ever adopted an existing industry standard. One might applaud if it were not for the investment in Lightning.None of that speaks to the needs of any serious audio production work, but it certainly will muddy the waters for headphone and headset makers. And I have not offered a complete answer as to the quality of this adapter. All I can offer at this time is that I plan to try building my own. We have a cable shop here, so I am wondering if we can do a better job with using off-the-shelf components, but my initial searches for shielded TRRS jacks did not turn anything up. FWIW, I intend to use this adapter for a while and see if the hum is a problem in a real-world recording. I think it may be okay, and beyond that, I’m not sure that any other adapter would be any better. Most of the sellers on Amazon aren’t even willing to commit to the CTIA standard, let alone reveal any technical details like shielding, so while this adapter may be imperfect, it may also be as good as one can easily get.