I’ve tried a few of those, I always get a buzzing or it gets weirdly hot, one just blew out my headphones. So I don’t really trust them at this point.

The big problem for me is that there is only one port, so you can ether listen to something, or, charge the phone, not both. Just having two ports would solve this.

Also, not something I really care about but a lot of people do, the headphone jack is an analog output, where as the USB-C is a digital output, and you need an analog signal to run a speaker. So they need to have their own DACs (Digital-Analog converter), and many of the USB-C headphones have poor quality DACs that loose detail. Used to be the DAC was just in the phone, and was generally of good quality.