Problem: Screensaver although installed, doesn't seem to work. The issue appears to be that xscreensaver doesn't auto-start. (Check in 'System Monitor' to see whether this is the case.)
If it is, in home>.config>autostart create an empty text-file called 'xscreensaver.desktop' and paste in the following information and reboot (then check 'System Monitor' again):
Comment=Screensaver for xserver
* Fill in red fields as necessary for your system.