is Apptrap safe for my mac?

It looks safe, but ineffective because it only looks at preference files. Those aren't the files you need to worry about. Never rely on any kind of "app zapper". Ideally, only install software from the Mac App Store. If you really need software installed from somewhere else, always make sure you know how to uninstall it should the time come. If the software asks for your password to install, be extra cautious.