Flash 3.8 is rad. Easily my daily driver now. Only downside is it's Gemini so sometimes it just keeps going until it wants to be done.
I have a few attention and finish mechanisms in my prompts. I have been using it for a week and a half and with some prompt taming it is great. (I have early access to the models cause I work at the place that makes the model). None of my attempts to ever tame Opus 5 have worked.