When comparing AppTrap vs Little Snitch, the Slant community recommends Little Snitch for most people. In the question“What are the best Mac OSX apps for someone that's new to Apple?” Little Snitch is ranked 7th while AppTrap is ranked 18th. The most important reason people chose Little Snitch is:
Little Snitch rules work even at login screen. Even when receiving attempted connection alerts, once logged in LS has stopped and requested permission for them.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Prefpane style app
AppTrap installs a daemon that runs in the background monitoring the trash, when you drag an app to the trash it will search for associated .plist files that have been left behind and ask to move them to the trash. In other words, AppTrap launches and does the work for you automatically. All you have to do is uninstall apps the old fashioned mac way by dragging apps to the trash.
Pro Protected even at login screen
Little Snitch rules work even at login screen. Even when receiving attempted connection alerts, once logged in LS has stopped and requested permission for them.
Pro Comparatively easy to use
Easier to use than traditional firewall software, but more powerful due to design and workflow.
Pro Protects your privacy
Protects your privacy and helps to prevent unwanted connections.
Cons
Con Not Supported in Big Sur
Con Gets some things, not everything
This is thorough enough in cleaning up most of the cruft that gets left behind by applications, but might not get everything for the more invasive applications, especially if some of the files have privileged permissions.
Con Requires using Finder
Does not work if you trash app using alternate file browser like Path Finder.