That's actually a useful test page for "did turning off everything in chrome://flags that says gemini actually work?" (it's reporting 148 and "unavailable" for me.)
Author here. After trying out the Prompt API over the last week, I wrote up some details on the chromium internals, how to use the API, and made some toy demos.
It's a 4 GB model that can be used to run on-device inference.