I can give you mine, since I use(d) opensnitch for a while.

It works quite well but requires a GUI (obviously), it looks like it primarily supports GTK. If you're hoping to use the machine purely from the CLI (like, when sshing into your work machine) it won't work well.

It is significantly less powerful than LittleSnitch, some options don't exist (like, allowing access to a domain), but you get similar functionality in many cases.

Overall, it's definitely worth testing out to see if it works for you.