I'd wager Kagi has a lot of benefit in learning and finding solutions to issues where you don't know the correct terminology AND in tech where a lot of non-tech content is available (f.e. analytics)
With chairs it's also less of a benefit in regards to productivity but health and comfort. I'm also still rocking a 150€ chair from IKEA, totally viable and comfortable, but I do see the benefit in a chair that has a lot of configuration options because I am slightly too large for mine. Still means one needs to know how to configure it properly (which is 90% of the health change)
Hard to quantify comfortability since it really indirectly affects mentality.
Then again, I'm not really using search a lot when working so Kagi is obviously also nothing for me