After viewing that website, I am now extremely curious as to the affiliation (or lack thereof) between “Objective-See” (the website you linked to) and “Objective Development” (makers of Little Snitch). Not only are some products drop-dead similar, but the company names are nearly the same! If there is no affiliation, then I am rather surprised there has been no legal battles between these two organizations, “open source” or not.
I’ve been a Little Snitch user for about as long as Little Snitch has existed. I never tried Micro Snitch though, so your link to that freebie site has me curious if I should install some of those Objective-See apps, especially since they appear to be free. There are some that support only MacOS 10.15 though, and since I am still on 10.13, I won’t be trying those.
I also use Little Snitch and have for several years now along side Kaspersky Internet Security. Doo you think that it would be overkill to be adding more. Those you mention sound good but just wondering. I am currently running Catalina 10.15.7 (still holding off on upgrading to Slur). Thank you for the heads up though.