It's a mixed bag, as it's still not stable (esp as very recently declarative support was added in what was likely a mostly-rewrite). But when it works, it works great (I've only tried on Linux and Android).

Neat. I'm skimming the documentation now and it looks like something worth keeping an eye on.

I have so many long-running scripts that I sometimes set up with TUIs or quick PyQt/PySide GUIs but the GUIs always seem overkill and the TUIs always leave me lacking. flet looks like a good in-between of the two.

I'd say it definitely makes building GUIs more simple and intuitive than the Qt and Tk frameworks at least. And very important for me, it's fully cross-platform (for the most popular platforms anyway). I must admit that the imperative style does start to become painful as complexity increases, which led to me dropping it for a while, and so the declarative update is welcome even though it takes some time for me to mentally grep.