This question gets asked with every new freeze, and the answer is always the same, because the Debian release cycle never changes. Unfortunately, that answer gets buried in two years of intervening posts.
So, for the benefit of other folks pondering this question, in no particular order:
- When Testing, under whatever codename, is about to freeze, it's true that maintainers often dump minimally tested code in to try to beat the deadline. So yes, right around the freeze date, Testing is at its worst in terms of bugs (including RC bugs).
- The whole point of the freeze itself is so that no new bugs can come in, because no new
code can come in. That's what makes the freeze the freeze. (Catchy name, huh?)
- For the next several months, the devs then focus their efforts on eliminating RC bugs from Testing. This extended, concerted bug fix effort is what makes Debian Stable what it is.
- During the freeze, the
only new bugs in Testing are those that occur when the fix for an existing bug triggers a different bug. By implication,
Testing only gets better once the freeze has taken place. Once "better" becomes "good enough," that's when what used to be Testing is released as the new Stable.
- So the only remaining question is whether an existing-but-still-unfixed bug affects a particular user. And only that one user can answer that question, and even then only by trying it (or through an extensive review of the buglist).
- As of the date of this posting, we are almost two months past Stretch's "hard freeze" date. Over the last four releases, the average length of a freeze is ~7.5 months. Simple arithmetic suggests that the current freeze is roughly ~40% complete. So a switch now is certainly a legit option.
- If practical, the safest course is to do a parallel run, installing "Testing" on some unused hard drive space, and giving it a whirl. If a show-stopper issue arises, switch back to Stable. Repeat as necessary.
That's the answer. And like I said, it never, ever changes. Additional information available on the pertinent Wiki page:
https://wiki.debian.org/DebianReleasesOne last tangential point: talk of "live testing" post-release is utter nonsense and betrays a complete ignorance of Debian's release cycle. The "live testing" phase of Testing's existence occurs
between releases, not
after a release. Once a new Stable is released, it does
not get routine bug fixes--that's why it's called Stable (once again, catchy name). The
only changes routinely applied to a Stable release are fixes for security bugs. The only time a bug fix is applied retroactively to a Stable release is in response to really, really critical/high profile bugs, and those are extremely rare.