I used Aeon from RC2 to RC3 iirc. Until the introduction of encrypted drives mashed my system and i suddenly had secure boot key problems or something. It was a year ago so I can’t remember exactly, but it worked beautifully until then.
So I moved on. But Aeon is really good, probably the best immutable desktop experience, if you can stomach GNOME as a daily driver (I couldn’t wait to jump back to plasma after I lost my Aeon setup). Richard Brown is opinionated but generally sensible about its development too.
I haven’t kept up with Kalpa development since last year, but the last I tried it was the same problem it’s always had; lack of development. It’s was years behind Aeon then and unless things have changed it’ll have likely gotten worse. The problems being that Rich Brown has great development and contributors to Aeon, while Mr Falken does not with Kalpa (or did not! Hopefully he has gotten some traction with it).
Good write up here as well from around that time. I haven’t had a chance to check out the article you linked though. https://sfalken.tech/posts/2024-06-08-how-do-aeon-and-kalpa-relate/