FWIW - I did a real world experiment pitting the built in Gemini Nano vs a free equivalent from OpenRouter (server call) and the free+server side was better in literally every performance metric.
That's not to say that the in browser isn't valuable for privacy+offline, just that the standard case currently is pretty rough.
https://sendcheckit.com/blog/ai-powered-subject-line-alterna...
It's worth mentioning that "Gemini Nano 4" is going to be Gemma 4, and presumably when it becomes the default Nano model, it should improve performance quite a bit.
(It's currently available for testing in Android's AICore under a developer preview)