I just spend two hours to install Little snitch 4, so I would like write my experience.
I had 3.8.x, so I downloaded 4.1.1 from site and not expecting any problems I install it, after reboot was all my network blocked, fans are running on high speed. Little snitch configuration app could not load either. In Activity monitor were all Little Snitch processes red. So after some attempts to do something I uninstall Little snitch and restarted macbook. After that everything worked, so I thought - ok lets try nightly build, it has to be good. Nope, after install and another restart I was in same place like before, so I uninstall it and restarted again. Then I wanted to try 4.0, maybe it will work. But could not find it, so I dowloaded 3.8. Then I remembered that when you uninstall little snitch, there was small window with check box for uninstalling configuration files. So again to install little snitch 4.1.1, reboot, uninstall (this time I checked this checkbox), reboot and then I installed 4.1.1, reboot. An then it finally worked.
I definitely didn't expect that this simple installation of version 4, which was released last year, will take me two hours. I expected that by this time most of bugs will be corrected and everything will be smooth.
Please put there some check that if Little snitch can't load configuration files, it ignores them or something similar. It will save time to quite a few users. Specially after Mojave is released.