mercury does not handle a full clear of system memmory automatically the close function is to use the "minize memmory when minimzing"
In generel i dot not advise to use the memory cleaning option because it should be handled by windows when needed. However recent testing has shown that there are some issues with windows memory handling of standby memory and Battlefield V5m and im working on something to fix that issue as well
You idea of a command line would not be bad I will implement som basic commandline support in the next version
in short: advise not to use memmory cleaners command line has been put on my todo list