I tried using it seriously 5 years ago. Things might have changed since then, though. All I remember is that it was tremendously slow and the results were pretty much garbage. It's an interesting project, nonetheless.

EDIT: They now have an online demo that doesn't require any installation. After waiting about a minute for peers to connect, queries ran relatively "fast" each time. That's an improvement. But the results are still junk, IMO.

https://yacy.searchlab.eu/Status.html

I gave it a try in 2017. I could live with it being really slow, but it didn't have any useful results for anything, so I moved on. Really like the idea, though.

Had a similar experience back in 2015 or so; I think that the idea of a decentralized web-scraper actually makes a lot of sense, but it just didn't seem to give me a result that was useful, and actually seemed to give a lot of porn results for perfectly innocuous searches. I ended up going back to DDG.

I played around with that years ago. Was absolutely useless at the time. Honestly doubt it has gotten much better.