Slowing down video vs higher framerate recording
By shooting at higher frame rate, you can achieve great looking and frame accurate slow motion. Interpolation is not going to happen. But if you want to slow down your footage beyond the frames you have, you can use the right tools in your video editor, or Twixtor plugin, but of course it will not give you as good results as a dedicated high speed camera. Absent frames are digitally interpolated. There are some more affordable Twixtor alternatives, such as Respeeder. These tools will give your video a smooth, high-frame rate look.