You are better off with a ND filter set for the Spark. PolarPro has a 3 pack and 6 pack for pre-order. I have always had good look with PolarPro ND filters on my P3P and P4. I went with the 6 pack as it includes PL, ND8/PL, ND16/PL, ND8, ND16, and ND32 filters.
DJI Spark Filter 3-Pack
DJI Spark...