I have the Future Impact. The C4 is easier to program and smaller.. If I had another chance I would pick the C4. Again not knocking the Future Impact. Its is legendary in some ways, but the C4 Source Audio answers all question with total professionalism and sounds great. Some mention Nathan Navarro. I believe he uses the C4 now from using the Future Impact. He is another not only a good bassist but he is super friendly and answers questions pretty rapidly.