But it won't let you just tile a single window to a side, it is mandatory to select another window for the other half of the screen. Also it moves those windows to a separate workspace for whatever reason, which causes a delay when entering/exiting this tiling mode because of the workspace switching animation.

I'm glad Rectangle exists. Now I just need something like Mission Control but with keyboard support (seriously, why can't I at least select another window with the arrow keys?)