I installed a Garmin Virb Elite Aviation Bundle in my L-235 in anticipation of the first flight, and the GPS function is already providing a wealth of information during taxi testing. (The Virb Elite is like a GoPro video camera, only with built-in GPS, accelerometer, and Wi-Fi.)

Just look at all this information! Ground speed, altitude, heading, distance, elapsed time, and in the lower right corner, a depiction of my position on the runway. My IAS at the time was ~55 KTs (63 MPH) and I had the flaps reflexed so as not to go airborne. So now I know that I can actually get to takeoff speed in 1,000' which is a good thing!

I originally mounted the camera on the rollover structure a few inches to the right of my head (as below), but have already moved it further to the right so as to have a clear view of the entire panel.