I used them for a long time before getting tired of appending !g after every search because DDG's results were SEO garbage. I'm trying them again and they seem to be slightly better, but I'm not quite sure. Also it appears that the minus operator doesn't work on DDG, and when I have to use it, I just do !s to search Google with Startpage (which I don't use because it's owned by an ad company and because its website is a little bit slower than DDG).