Leap is their stable distro, and shares binaries with SLES, their enterprise offering.
Both Leap and Tumbleweed have BTRFS by default, with Snapper for automated snapshots at upgrade and boot. Update messed something up? System won't boot? Just run an old snapshot until it's fixed. Zypper, the package manager, has state-of-the-art dependancy resolution, personally the best I've used.
They have a number of extremely interesting spinoff projects: MicroOS and MicroOS desktop (recently renamed, but the new names are escaping me) which use immutable root filesystems with automated updates and native Podman support. Snapper integration shines there, as well. If it fails to boot after update, it'll automatically roll back.
They're doing quite a bit, and it's all culminating in being very useable. Tumbleweed is the crown jewel, though.