Actually, I like kscreen. The desktop display configuration interface is clicky, draggy and intuitive, and apparently they store settings for specific external monitors by EDID and feed them into xrandr once you connect the monitor.
Enter my Zenbook, various microHDMI to VGA/HDMI dongles, external monitors and projectors. What happens, usually 10 minutes before an important presentation, on a bus without internet and my boss getting antsy, is KDE presenting me with a black screen and the mouse pointer stuck at the top screen edge. Panic mode fix: create a new user from the terminal. In the end I was stuck with 3 different temporary user accounts and no graphical interface unless the µHDMI to VGA dongle was plugged in. Don't judge me, I was overworked.
Still, the troublesome configuration had to be somewhere in my home directory, so I needed to do some more creative renaming, i.e. .kde to .notkde, restarting sddm and praying to the deity of the moment.
Kscreen's config files happened to be in ./local/share/kscreen, I just deleted them all, problem solved.
Got a kernel update in the process and now I need to consolidate user accounts…
Update: As of 09/2020, kscreen still has problems with dongles. (PD USB-C hub with HDMI, XPS13 with BenQ screen) I got sick of constantly nuking the config files and tried apt remove kscreen. Config files still got written. Turns out you have to disable the kscreen service (System Settings->Startup). And now I'd better get used to Xrandr.
