Konstru stores all model data in millimeters but this doesn't affect what you are working in because Konstru translates on download into platform document units. So let's say you are working in ft in Revit and you are uploading to Konstru, you Konstru model will be stored in mm. If you download it, you'll still get ft. It doesn't matter if your coworkers are working in meters, if they download a Konstru model it will be translated into their local units and back once they are uploading. So every Konstru user can work in whatever units they like.