3 Answers. You’re right, Debian stable does not have a rolling release model in so far as once a stable release is made, only bug fixes and security fixes are made. As you said, there are distributions built upon the testing and unstable branches (see also here).

How unstable is Debian testing?

Testing has more up-to-date software than Stable, and it breaks less often than Unstable. But when it breaks, it might take a long time for things to get rectified. Sometimes this could be days and it could be months at times. It also does not have permanent security support.

Is Debian worth testing?

Debian testing is probably best option between spoon-feeding systems like Mint and diy like Arch. The packages aren’t on the bleeding edge but you don’t really need to worry about spending weekend in configs. Make a live USB or a virtual machine and try it out.