I've used them before, and they work aside from a lack of integration with other programs. Same as any other isolation system (like Snap).
My main problem is a lack of digital signatures on the packages. Deb, RPM, everything else is digitally signed, and has been for a long time. Flatpaks should be signed too.
I just need xdotool. ydotool is missing almost everything. I don't need programs sandboxed from each other. I don't need that multi-DPI stuff (200% scaling works fine in X). Wayland doesn't provide any features I'm missing.