I honestly think FastGPT is the best implementation of AI w/search, and is extremely versatile/useful across domains (granted I don't code). I think it's the same thing as the Quick Answer feature from their standard search.
In my daily work as an MD it's become my reflexive go-to for looking up answers to specific to general, easy to complex clinical questions. I use it far more frequently than UpToDate (which is no less than the holy book of medicine), more than PubMed/Google Scholar searches, and definitely more than a basic web search (Google, only b/c it's a hassle to log in to Kagi every session at work).
Maybe 1 time out of 10 it won't give a correct or meaningful answer (in which case my prompt needs to be refined, or is just not suited for this kind of tool). But apart from that it will give me exactly what I need, because it uses Kagi search to source its answers. Kagi search does a decent job bringing to the top relevant journal articles (which in turn may mention other articles, adding indirectly to the trove of sources FastGPT pulls its final answer from). It shows the 5 search results it referenced at the bottom of the page, so more often than not if I don't get my answer in the direct summary, I have very relevant sources to read through.
I also don't think you need a Kagi account to use it.
Sourcing information from better search results. I cancelled my Perplexity Pro since for any use case I had for it, I would instead use Kagi FastGPT. I tried Assistants (beta) but I didn't think it was anything special, didn't really see a way to integrate it as a daily tool, and ultimately FastGPT gave me the best answer, even better than their gpt4o and Claude Opus/Haiku based assistants.