Even Debian unstable is reasonably stable for me (despite the name), comparable to other rolling-release distros I think. Really not-ready-to-ship stuff is uploaded to 'experimental' instead. The main precaution I take is having 'apt-listbugs' installed. It checks for any new high-severity bugs in the packages you're upgrading. You can take a look at them before deciding whether to upgrade, which occasionally helps avoid installing something broken.

On servers I prefer Debian stable though. I like my mail server running unattended with only security upgrades, and rolling-release distros tend to introduce config-breaking changes exactly when I have the least time to deal with them.

You're describing my setup exactly. Stable for servers, testing for personal machines, with apt-listbugs installed (the install guide recommended this at one point, not sure if it still does). I also ran unstable for about two years and, like you said, it was fine.

Testing is usually only a few weeks behind unstable though, so if your primary motivation is to have relatively recent software and a rolling release so that you never have to stop everything and deal with full system upgrade breakages, then testing is great.