I’ve never felt I was getting inferior search results but some people claim they do. I think the way it works is Startpage for example actually takes your search request and uses Google, Bing, and Yahoo to get the results but the search comes from their servers, as far as those engines can see, then Startpage presents it to you. So Google never sees what IP address originally made the request. Then Startpage deletes the whole event within 24 hours, or something.
They may filter the results before they present it to you, like eliminating sites they’ve identified as worthless plagiarizing of legitimate sites, but I don’t think they censor anything above what their source engines do. I have never said, “Gee I’m not finding what I’m looking for, I’d better go directly to Google.”
Startpage servers are located in the Netherlands so law enforcement can’t get a prospective warrant and force them to keep your data to turn over to them (without going through Dutch courts) HOWEVER Netherlands is in the 9 Eyes, which means they have an alliance with our intel community, which means Startpage can theoretically be forced to rat you out, if somebody wants to claim you’re an international terrorist or child pron trafficker.
I think DuckDuckGo is located within the U.S. so even less protection. These shouldn’t be considered anonymous security when it really matters, just a way to cut down on the amount of data being compiled and stored on you for marketing purposes.