Fedora's missing Chromium updates

Debian sid / unstable is the rolling development version, and can be a perfectly usable distro (though not really a "release") depending on your requirements. You can install a complete, working system using only packages from Debian sid—there is an installer available (the Unstable "mini.iso"), though no full CD/DVD images due to the rate of change. It's "experimental" which is exclusively for staging and doesn't include all the packages needed for a working system.

One could say that sid / unstable is the staging area for the testing release, in much the same way that testing is the staging area for stable. That doesn't imply that it "is not a distro version meant for use"; it's meant for developers and beta-testers to use. Those who are less tolerant of typical bleeding-edge development instability will still want to use the testing or stable releases, of course, and these are both kept more up-to-date than they once were.