I think this looks amazing. I do like the behaviour of tiling WMs, but having a DE is too comfy for me to give up. This could possibly bring the bestof both worlds.
Krohnkite went unmaintained a while ago, which is when Bismuth forked from it. So, Bismuth is basically a straight upgrade. The dev implemented tons of features, which you may or may not need, but I think, there were also some fixes for stability and Plasma version compatibility.
Polonium came about, because Plasma 5.27 introduced a (manual) tiling system of its own, which partially broke Bismuth, but also meant it made sense to develop a new KWinScript, which makes use of this native system.
As such, it is a step back from Bismuth. I think, it's roughly comparable to Krohnkite in terms of features now, but still a very young project, so not as stable yet...
I've tried all 3 and krohnkite felt like the more polished, can't tell you which doesn't do what but the others felt a bit clunky in the way they handled resizes and such
I really can't stress how good PaperWM is in combination with a touchpad. I wouldn't recommend it at all on a mouse-only environment, but when you can use multitouch gestures to scroll through the workspace it works really well.
Chiming in with another great alternative, Tactile lets you tile windows and stack at the same time. Between the Tactile hotkeys, Alt+Tab and Alt+~ I never need to use the mouse for window manipulation anymore.
You could try Pop!_OS. There you get the full DE, plus tiling implemented by a GNOME extension. You can also just install that extension, of course, or another.