Bismuth is better for those of us who want dynamic tiling.
Unfortunately, the developer no longer wants to maintain it, and while it's still working through KDE gaining a tiling API (that doesn't do anything dynamically, also what Polonium uses) for the most part, who knows how long it'll last...
Bismuth was broken for a while on KDE 5.27, which opened space for Polonium to gain some adopters. There's a long thread about the future of Bismuth. Unless someone else takes the lead, it'll be unlikely it'll keep working reliably on Plasma 6 and Wayland, at least during this transition phase.
Hmm for now I encountered no errors, but I'll consider Polonium and seeing if I can use another light wm (although TBH I don't know this world that much, so I don't know what nice wm exists that has this kind of cycling layouts behavior)