Disclaimer: I'm the developer of Little Snitch for Linux. Regarding MITM concerns: The eBPF component, which actually sees all the traffic, is Open Source (GPLv2). You can review it on Github and verify whether it sends any data to user space: https://github.com/obdev/littlesnitch-linux

But the trust issue is still real, the daemon has to run as root because it needs to watch for new mounts and keep a table of file system roots up-to-date, even after loading all the eBPF programs. As a root process, it can technically do whatever it wants. Unless you limit it with a kind of mandatory access control (SELinux or similar).

This is the very first release and we will probably come up with a more restricted permission requirement in the future. For the moment, I try to catch up with bug reports. There seems to be more diversity in the Linux landscape than I had expected.