What Dreame’s arm has that Roborock’s doesn’t (yet) are attachments. Dreame showed off a small toolbox that stored two brushes — a sponge for wet messes and a bristle brush. The idea is that the robot can attach these to its arms and then get into nooks and crannies the main robot can’t. I didn’t get to see the robot actually do any of this, though, so it's all still a concept.