> tell me the dirt on DDG / webkit
On DDG I think it's not proper FOSS, it's some kind of "freeware".
Regarding other webkit-based browsers, the main one of course is Safari which is also not FOSS. The closest one to being and usable while also being FOSS I think is GNOME Web, formerly Epiphany. But that one is just not good enough, I think it lacks some "must have" features.
To summarize, webkit-based browsers are either not FOSS, or too far from being usable.