It looks similar with the difference of scrolling. Kind of interesting, and you still can have stacks of windows. But how does it decide on how wide a window should be?

Usually you'd have some predefined widths, like 33%, 50% and 67%, and use a shortcut to cycle between them. And you can define window rules to start some applications with different width than your default.

edit: and as fellow niri user, I recommend people try it. I think it's one of the easiest tiling WMs to get into, it feels very natural within minutes.