Did people sleep through the bit about Universal Control?
There is simply no way to do this on Windows, for example, without a KVM switcher box. There is no software that lets you move your mouse over to another computer by simply moving the cursor to the edge of the screen and it just pops over like it. Same for the keyboard. Devs have tried and it doesn't work. There are apps that have tried and it never works right, drivers are a mess, and it never works, let alone consistently. You'd have to get a KVM box and hit a switch that moves the keyboard and mouse's cords in a switcher like fashion over to the other machine. Let alone a tablet.
It is certainly a very cool feature. I'm just struggling to figure out how often I need it. I don't regularly work with multiple machines like that. But I'm sure there are plenty of people out there that do.