I’ve only had the 4C a couple days. I’m using it along with the Expert Mouse. I use either one, depending on what I’m doing. I try to use the 4C to avoid switching to the mouse and then back. Eg, while coding it’s nice to be able to type, click somewhere, and type some more without grabbing the mouse or jamming on the arrow keys. If I’m going to be mousing for a while, I’ll use the Expert Mouse. I also use the Expert Mouse scroll wheel for scrolling.
It’s very fast to switch windows by look-clicking the Windows taskbar at the bottom of the screen. It’s also very fast to switch tabs by look-clicking. Both of those actions tend to be accurate because they are on the edge of the screen. If eye tracking chooses a point off screen, Windows prevents the mouse cursor from leaving the screen. This means I can just look, press, and release capslock and it almost always does the right thing, without needing to hold down capslock to use head tracking.