Be more specific. How is it not working? .. black screen, error message, etc. .. and provide a Kodi debug log.
"kodi-send" does not give any kind of succeed or fail indication.
That's true and probably something which could be improved. No promisses it will be
But the screenshot problem seems to have cleared up after a reboot, so I cant reproduce it now.
On other Kodi installations (on Ubuntu for example), there's no default screenshot folder set and by running that command once you'll get a dialog which asks to which folder those screenshots should be saved. After selecting a specific folder, and directly after you selected it check the guisettings.xml, you will see that this setting is not stored yet. It will be written into guisettings.xml after a reboot. Normally it should have a direct effect, but sometimes a reboot/restart helps in those cases.
Normally, if Kodi logs, that something is written into a specific folder, it should be the case that it's like that. Otherwise you would see a log entry that writing that file failed for whatever reason. As you can't reproduce that issue anymore, I guess we can see this problem as solved.
If you have other problems, the context menu for example, please share a debuglog which shows the button presses you normally do to bring up the context menu. We can't do anything without a logfile and we would not like to 'guess' 
