FWIW, I switched from an iPhone 4 to a Z3 Compact because it was the only decent "small" phone available. But a 4.6 inch screen is not actually "compact", as far as I'm concerned. I switched back to iPhones for the SE, which isn't that much physically smaller, but is a lot more usable nonetheless.
It turns out the important dimensions are the overall width (for being able to hold it one handed) and the screen height (to reach everywhere with your thumb), and the iPhone SE's top and bottom bezels don't screw up either of those.
With the Z3C you can hold it one handed, but you can't use it effectively unless you have gigantic hands. Making a phone fit in one hand isn't enough; if the entire face is covered with screen then it still takes two hands to operate it.
It turns out the important dimensions are the overall width (for being able to hold it one handed) and the screen height (to reach everywhere with your thumb), and the iPhone SE's top and bottom bezels don't screw up either of those.
With the Z3C you can hold it one handed, but you can't use it effectively unless you have gigantic hands. Making a phone fit in one hand isn't enough; if the entire face is covered with screen then it still takes two hands to operate it.