We have been using radar in the US for several years. They both have about the same overall accuracy. The main objection to radar is that it gives a peak value rather than an average over a distance. That was very clear when you watched the radar gun as the Duck was approaching. We chose radar for several reasons.
Radar is easy to set up and calibrate.
There is tractability of the calibration to the National Institute of Standards and Technology. Radar also has a long history of holding up to court challenges in the prosecution of speeding tickets. When used properly, it is very unlikely to give false readings. Radar also updates quickly so we were able to record multiple readings on many runs. It can be pointed at the incoming boat no matter what direction it is coming from.