MicroOS and its derivatives are all based on Tumbleweed. MicroOS was intended to be used for container workloads. Aeon grew out of that with a GNOME desktop, Kalpa a KDE desktop. Because they were focused in a way Tumbleweed is not, they are a more opinionated distro. On the other hand, Tumbleweed is a rolling distro that wants to be all things for everyone.
I guess you get the atomic system, but with Tumbleweed you get snapshot backups anyway.
One of the main advantages of Tumbleweed is the extensive testing pipeline. I'm not sure how a derivative would be able to offer a similar experience
Absolutely wrong.
Tumbleweed is a conventional distro. You're root, you can do whatever you want, you have full R/W access to the entire FS, and updating is by installing lots and lots of packages into the live OS while it is running.
Aeon and Kalpa are immutable: the root fs is largely R/O even to root, and you cannot install or update packages on the running system. To install packages into the OS itself you must reboot, and installation is transactional -- it can automatically undo changes that prevented a successful boot.
Kalpa is the KDE desktop version of MicroOS.
Good explanation, but note that Tumbleweed can use transactional-update with btrfs snapshots like MicroOS. Updates are still applied live though.