xfwm4 version 4.13.1's help text says --vblank=present is trendy but it's not, a x is apparently required:
$ xfwm4 --help
--compositor=on|off|auto Set the compositor mode
--vblank=off|present|glx Set the vblank mode
--replace Replace the existing window manager
$ xfwm4 --replace --compositor=on --vblank=present &
xfwm4: Unrecognized compositor option "present".
Type "xfwm4 --help" for usage.
$ xfwm4 --replace --compositor=on --vblank=xpresent &
Waiting for current window manager (Xfwm4) on screen :0.0 to exit: Done
should be easy to fix by adding the x to the help text
I guess I should add that " --compositor=on" doesn't actually do anything at all if compositing is set to off in the settings while " --compositor=off" actually turns it off when it's on in the settings. This is a bit confuse.
Already fixed a while ago https://git.xfce.org/xfce/xfwm4/commit/?id=85c8a57