In a previous life I learned a fair amount about electronics as a Ham radio operator. One of the things I learned was about frequency measuring meters to measure radio or signal frequencies or Hertz. Different meters had different amounts of "smoothing". If a meter actually displayed the instantaneous frequency the numbers would jump around so much (because the frequency of a radio signal really does not exactly stay perfectly at one frequency) the operator would not be able to read it. Some meters the smoothing was adjustable, depending the application.

I think this is probably the situation for the output of speeds, be it gps or radar. If too much smoothing is used, real changes in tractor speed will not be reflected quite as quickly. If too little is used, erratic readings cause the speed displayed to jump around and may cause controller problems, with the controller trying to follow this erratic speed. Whoever manufactures the speed device has to make an engineering decision of how much smoothing to use. Different brands could act slightly different because of this.

John