Free and Open Source Software

I'm not the one you asked your question, but I think I understood what they meant.

First of all, technically MicroOS is the non-desktop version of openSUSE's take on an atomic/immutable distro. The desktop variants are referred to as Aeon (for GNOME) and Kalpa (for KDE).

Secondly, while Aeon/Kalpa definitely is to openSUSE what Silverblue/Kinoite is to Fedora, there's a clear difference in vision and maturity.

Vision

Fedora Atomic is a very ambitious project; everything points toward it being Fedora's take on NixOS. But, unlike NixOS, it couldn't start from scratch nor did they intend to. Instead, it's the process of evolving their existing products into something special. As such, it has been over two years since Fedora has even explicitly stated that they intend for Fedora Atomic to become the default eventually (without saying anything about sunsetting the old). While, AFAIK, openSUSE has yet to make similar statements regarding Aeon/Kalpa.

Maturity

Everything points towards Fedora Atomic being more mature than openSUSE MicroOS; work on the project has started earlier, Fedora Atomic is almost done with their transition (from image-based) to OCI while I don't recall openSUSE mention anything regarding their transition (from 'snapshots') to image-based since they mentioned it briefly last year. Furthermore, Bazzite (based on Fedora Atomic) has become the face of Gaming Linux while openSUSE' MicroOS fails to deliver on anything but Aeon. Which, to be fair, is absolutely fine. But not everyone is fan of GNOME.

So, use Tumbleweed if:

• You prefer the traditional model
• You like YaST
• You like the rolling release model and not being tied to GNOME

Use Aeon if:

• You like GNOME and an atomic distro on a rolling release distro
• You prefer the opinionated, hands off, little to no customization path that openSUSE has currently chosen for its Aeon
• You like a containerized future

Use Fedora Atomic if:

• You want an atomic distro, but don't like any of the decisions made for Aeon; i.e.
  • prefer to use KDE, Budgie or Sway (or any other desktop environment through uBlue)
  • aren't that big of a fan of container workloads
  • prefer having the choice of installing native packages
• Prefer atomic on top of a point release distro

Finally, regarding containers specifically; let's say you want to install package X.

• On Tumbleweed, you just do sudo zypper install X and you're done with it.
• On Aeon, if it's available as a Flatpak, you do flatpak install X. If there's no Flatpak of it, you install it within a container that you access through Distrobox. Within the container, use the package manager corresponding to the container. Technically, while inside the container, the environment is very similar to Tumbleweed. So, say you got a Tumbleweed container, then you can continue using sudo zypper install X.
• On Fedora Atomic, you can layer onto the system through rpm-ostree install X; this is very close to how installing packages work on Tumbleweed. And, you can continue using both Flatpak and Distrobox; like how it's done on Aeon. Note that Tumbleweed also allows access to Flatpak and Distrobox. So, Aeon is most restricted as it can't install packages onto the base system. Btw, Fedora Atomic accomplishes this through layers that can also be peeled off later on (through uninstalling for example). With this, the base system actually isn't affected, but the end user doesn't notice it.