The joint flybe/Stobart Air press release states "six new routes to Northern Europe and Benelux countries". Now it all depends of what flybe/Stobart Air consider Northern Europe to be, but if we look at what United Nations and the European Union defines as Northern Europe; Germany isn't a part of Northern Europe. Northern Europe is the Nordic countries (minus Greenland) and the three Baltic countries. UN and EU don't agree about the status of the British Isles - EU include the British Isles in Western Europe while UN will have the British Isles to be a part of Northern Europe.
If we consider flybe/Stobart Air know what Northern Europe is, then we may be talking about a very few airports: airports in Denmark (EBJ and AAL are the only with no flights to STN), airports on the south west coast of Norway (SVG and BGO) and one airport on the west coast of Sweden (GOT). All these airports mentioned are less than 600 nautical miles from SEN, which I think a maximum leg length should be for the ATR.