I can tell you that I've been using Kagi for a few months and it hasn't been life changing or anything. But I would say that it has been useful enough to keep around. I honestly like the info dense layout over the other search sites, and I use the ability to push down or block sites entirely so I don't see the spam sites I don't want to see. Also, "quick answers" is actually pretty useful sometimes when I don't want to click on any of the search results. Plus, with the $10 sub, you get unlimited uses of the summarizer, which has been great for arxiv papers.

I wouldn't say it's for everyone and I don't know if there's astroturfing going on, but it's been useful enough for me to keep paying the $10 a month