Unfortunately, they're not great to use with a phone in your pocket, since then the motion of walking around will adjust the knob and change the volume.

Although, come to think of it, I could probably just glue the knob into a fixed −10 dB of attenuation and then use software volume control to change the volume.

I have also noticed that those passive inline volume knobs tend to adjust the right and left channels by different levels, especially with low-impedance outputs like IEMs, but that might because the ones I've bought cost ~US$2 from AliExpress.

I could probably also fix the issue by buying a worse/less-powerful USB-C to 3.5mm DAC. The official Apple one is pretty well liked by the audiophile community, since it's powerful for the price, which is great if you have high-end headphones, but horrible if you have earbuds/IEMs.

Weirdly enough, the same Apple USB-C to 3.5mm DAC is much quieter on Android, since it defaults to a low hardware volume on the DAC, and Android then only uses software volume control to lower the volume, see https://issuetracker.google.com/issues/242221770.