I can't recommend Zenfone 8 at this point. Asus has removed all updates from support page and you just have to hope that you get those at some point thru phone updater.
So if you buy 8 Flip, you might be stuck with older version of android.
But if you don't care about those updates i guess it is as good time as ever. Hardware is still good and fast. Reception is really good and i love that you can force 4g network only (there isn't 5g where i live and 3g is slow as hell). Flip mechanism is still awesome and really usefull.
Is there even Zenfone 9 Flip version? I thought there is only the smaller Zenfone 9.