I find the fast models good for rapidly iterating UI changes with voice chat. Like "add some padding above the text box" or "right align the button". But I find the fast models useless for deep coding work. But a fast model has its place. Not $50/month though. Cursor has Compose 1 and Grok Code Fast for free. Not sure what $50/month gets me that those don't. I liked the stealth supernova model a lot too.
Cerebras makes a giant chip that runs inference at unreal speeds. I suspect they run their cloud service more as an advertising mechanism for their core business: hardware. You can hear the founder describing their journey:
https://podcasts.apple.com/us/podcast/launching-the-fastest-...