A samsung galaxy s4 is really does live now be considered the best smartphone in the world. The design of the buttons has barely changed. The S3 wasn’t big on buttons, sporting only a volume rocker on the left edge and the power button on the right.
The eye scrolling only works with the default samsung apps. For instance, it works with the default browser but not google chrome. It also needs you to be looking at the middle of the screen and the light must be perfect to work. It is actually also not eye scrolling but rather head scrolling. If you tilt your head or phone it scrolls. Not worth using and it messes you up more than it helps. Works in the email app too.
It doesn't track your eyes, it tracks you head; closing your eyes or turning your eyes away won't do anything. You have to move your head side-to-side up-and-down. It also depends on the lightning in the area you're in, if it's dark then obviously it won't be as responsive; same goes with really light environments.