Personally, I find it returns much better results than anything currently available elsewhere. It reminds me of a time when search actually worked. Also, no ads and no tracking.
BTW, different instances can supply poorer results than others, so shop around to find the best one for you.
I just tried it with a few different instances, the fact that you can search the web for files is awesome. Just one problem though, I tried searching for a few specific websites in the "general" tab and they just wouldn't show up in the results.
People don't like the idea of paying for stuff they're used to getting for free
Privacy Guides does not include Kagi in their recommendations because an account is required in order to search, despite it being against their privacy policy to log, and despite the fact that they allow "no-log" VPNs, messaging apps, etc. which all require accounts. They're starting to soften to Kagi with their new Privacy Pass feature, however they seem hung up on the fact you need an account to generate private tokens. Accounts can be made with burner emails and paid with crypto.
Kagi leadership has had some controversial opinions on search censorship (they're fairly blanket opposed to it) and other social issue in the past
In addition to search, Kagi offers AI tools, which is a turn-off for a lot of people
To me, none of these things are deal breakers, but some folks are eager for an excuse to complain.
They built their own index, but if the search engine can’t find what you’re looking for, they have an option to show you proxied results from Google or Bing.
I'm more biased against Google than against Microsoft, and as mentioned in another comment, the search engines are proxies of the respective companies, so it's hard to give an objective opinion.
Now, what I would suggest, trying to be as neutral as possible, is to test both and see which fit your needs more. After that, use mainly the better one and keep the other as a fallback option.
I use several search engines. All have their + and -. As main search I use Andi, apart Startpage, Mojeek, Whoogle, Ghostery Search, Groot and some others, apart some specific ones, like Forums, Pixabay, Wolphram Alpha,, etc., I find what I'm searching for. Multisearch engines are fine, but they don't show the same results of the engines which API's they use.
Apart of privacy, it's mayby more important to avoid search engines which logs the searh history, because the filter bubble effect, causing an biased information.