[...]
And as far as I can tell regarding the search results, history, visited website using the DDG results or its browser/extension really affects the search result's order and vastly the whole SERP. Also, DDG not only use bing algo but also from yahoo and yandex, although yahoo is also fed by bing so it just the same.
I tried DDG before, while it's good for privacy, I don't think it serve as a the best search engine, base on it's results, it still lacking, if they can improve that not just by compiling its search results from those other search engines then I might reconsider using it.