The main difference between these two gimbals would be the SHIFT is definitely a consumer product while the SP-PRO Gen. 2 is a professional's product. The reason for this is the SHIFT is made out of plastic while the SP-PRO Gen. 2 is made out of airplane grade aluminum meant to outlast your cameras. In terms of performance and ease of use they are on par with one another. However, the SP-PRO Gen. 2 has a great advantage on durability over the SHIFT. If you are looking for a gimbal for professional use, the SP-PRO Gen. 2 will handle the day to day wear and tear better than the SHIFT. The SHIFT is meant to be a more affordable product for your average consumer that would like a high tech gadget for use during special occasions or trips.
In addition, the only other difference in these two gimbals will be the SP-PRO Gen. 2 has a scroll wheel vs a zoom lever like the SHIFT. This scroll wheel will allow you to adjust camera features from the handle of the gimbal such as:
Although, these features are still adjustable when using the SHIFT, you will need to adjust while touching the screen of your phone vs from the handle of the gimbal with the SP-PRO Gen. 2.