I stumbled across the feature a few hours ago. I had asked Gemini why there's a hole in the middle of the city of Azusa, topologically speaking. It had given me a useless tautological response: because they never annexed it. Then it offered to create a research report and I agreed. Five minutes later I got a notification on my mobile that the report was ready. It had 120 sources including assessor's maps, historical maps, court cases, and narrative articles. The text that went along with it was too verbose and still contained paragraphs of vague stuff, but it had key information linking the Mexican land grants, the founding of the city, and other events of history. Very impressive.