I work professionally as a colorist and the blackmagic cameras aren't professional cameras. They just don't look nearly as good (especially in difficult scenarios) and the footage is far less flexible than arri, red, or the high end sony venice line.

The only projects that use them in my experience are low budget music videos (I'm talking very low budget - typically sub $10k) and documentaries. Occasionally you'll see them as a C cam for higher end jobs.