The placement is pretty good for me. But the critical key is I have it set so that one click does nothing when not in the camera app—I have to double click it to launch the camera. One click would cause too many accidental camera launches.
Once I’m in the camera app, the Camera Control is also in a good position for easy access. There are two ways I hold my phone (16PM) when taking a picture, both usually one handed. One grip is pretty much like a normal vertical phone—so as a right hander, with my thumb on the right edge of the phone and my fingers on the left edge, but my hand shifted down on the phone a little so the bottom right corner of the phone rests on my palm/base of my thumb. In this position the Camera Control is within easy reach of my thumb. I can easily rotate my phone to horizontal orientation with this grip, but with my elbow sticking out a little awkwardly. If I know I want to take a horizontal photo/video then I grab my phone (still vertical) with my thumb on the left edge and my fingers on the right edge with my pointer finger resting on the Camera Control, which makes it natural to hold horizontally. Likewise, I can easily rotate back to vertical with this grip but I have to tuck my elbow in which gets a little awkward again.
I’d say the major advantage of Camera Control is a completely consistent way to launch the camera app no matter what state the phone is in (screen on/off, lock screen, home screen, using an app, etc). Maybe this can also be done with the Action Button, but with the Camera Control once the camera app is open I also find it convenient to just keep my finger/thumb on the Camera Control to switch cameras if needed and press the shutter. From launch to shutter is very fast so I’ve been able to capture extremely fleeting moments that I’m not sure I would have caught as well otherwise. It’s gotten so I pretty much only use the Camera Control for the camera now. But at the same time, I don’t think it would be the end of the world if I had to make do with just the Action Button.