I would say stick with the ATSU you are in contact with, if you switch frequency without telling them and then they can't raise you or you act eratically then they will try and trace you - requiring lots of phone calls - and maybe vector aircraft away from you. Increasing the workload. Also the controller you are talking to might be better suited to help than D&D. After all D&D are only located in the centres and approach controllers will have (possibly) a greater local knowledge