Apologies for a slight mis-communication. I was not advocating or indicating I use all of them at the same time and spend all of my time looking at them.
I spent a few minutes on the highway / road, with a competent passenger and we used the devices to check the speed displayed on the other systems against what was displayed on the speedo. This provided a good indication of what the 'real' speed of the vehicle was as opposed to the displayed speed on the car speedo.
For example in one car the speedo reads 113kmph but the actual speed via the other devices is closer to 109kmph.
If you are going to grumble and gripe about a $200 ish fine, send some time to do some preventative actions.
