I find it does well with ebooks. I haven't tried with pdfs or videos. The quality of the AndiSearch summaries for the things I use every day like articles, Wikipedia and technical documentation is very good.
The Summarize button is on the search results, therefore you don't need to visit a separate site and paste in the url. Additionally, you already know when a summary is available as the button only shows when it is. It is new but already I feel that it changes how you use a search engine having this feature available right there on the results.
The Kagi one said 'No summary available at this moment, please try again later.' for many of the urls I tried.
I am (obviously) copying and pasting the same urls that appear in the search results I shared individually into the url entry form on the Kagi summarizer page.
Also, being realistic, I do not believe that many normal people try to summarize the full text of old public domain ebooks. If you search for Moby Dick, much better resources come up, and that is what you want a summary for. People want a summary when they are searching to know if they should read more.
Summarizing long articles, videos, etc. is why these summarizers are so useful, you talk about web search but what OP linked is not a search engine (the Kagi search engine is, but this demo is not, it is just a summarizer that you use if you already have, for example, an article found on HN), you are talking about two different tools.
The Summarize button is on the search results, therefore you don't need to visit a separate site and paste in the url. Additionally, you already know when a summary is available as the button only shows when it is. It is new but already I feel that it changes how you use a search engine having this feature available right there on the results.
The Kagi one said 'No summary available at this moment, please try again later.' for many of the urls I tried.