From my experience (albeit 20 years ago) Debian testing was basically unusable since it could get into an unworkable state quite easily. You were much better off running unstable instead if you needed the absolutely most recent versions of stuff. It would still break occasionally but would get fixes would be available much sooner.

Backports are quite variable. Distro packaging systems are really awkward for software from language ecosystems with many dependencies. I end up having to install a static build of podman if I want a recent version. A backport basically seems impossible.