While I won't deny that this may often work, I disagree that it's a good idea, and that `apt` being smart is sufficient to guarantee that this works (or keeps working in the future).
Pinning specific packages from `testing` or `unstable` is explicitly discouraged, for very good reasons covered by this classic link: https://wiki.debian.org/DontBreakDebian#Don.27t_make_a_Frank... .
Arguably, the backports kernel is the right choice to get a newer kernel on Debian Stable. Indeed, in the past, the backports kernel could take awhile to update, but no more - case in point, `trixie-backports` currently contains `7.2`, same as `unstable`.
Either way backports does sound like the best option, sure.