Fluid tile does not replace the KWin tiling system, just adds more auto-tiling features. Krohnkrite and Karousel replace the current KWin tiling system Fluid tile works with KWin tile editor (Meta + T shortcut), this allows better integration with KWin without needing to create another tile editor as is the case in Krohnkite, additionally, you can use the shortcuts that come with KDE by default to move windows, and expands functionalities such as changing the tile layout with shortcuts, etc.. The idea is to adapt to the KWin tiling system, not replace it