(initially written as a reply for https://kagifeedback.org/d/4727-option-to-choose-or-exclude-specific-external-indexes which seems related, but really this thread is more appropriate)
As a very recent Kagi user (I've started using it only today), I've both been pleasantly surprised with the features (lenses, ranking adjustments, inclusion of web archive results, etc.) and a bit miffed by the "All results from external indexes" shown on my first few searches.
My immediate first reaction was "isn't its own index Kagi's main selling point?", then I read https://help.kagi.com/kagi/search-details/search-sources.html which makes sense, but does not list all sources, and especially not Google, Bing, Yandex, etc., nor any "average proportion of Teclis-sourced results that can be expected". (ok, you advertise very little telemetry, but surely you anonymously gather that information on the backend's side, right?)
My immediate second reaction was "ok, if All results from external indexes
, then which ones and which result comes from which index?"
I can understand DuckDuckGo not showing the source index as it's targeted to mainstream users who might satisfy themselves with "most results come from Bing, some from Google, others from elsewhere" (or who might be plenty satisfied by believing DuckDuckGo has its own index, for that matter).
But Kagi seems targeted at power users who might want to know more.
Having the possibility to configure the used indexes would be ideal, of course (a feature lenses somewhat provides, but not at the index level), but simply listing from which index each results comes from e.g. in the "shield popup" (not sure it's called that), with an option to show it right alongside the URL, would already go a long way.
Not a dealbreaker for me, but if it was implemented, it might be a good reason for me to immediately subscribe without ever looking at, say, self-hosting a SearX instance (I'll probably still become a paying Kagi user, just because of the features Kagi already has, which seem already superior to ad-based alternatives).