I usually measure the wind speed in kph (kilometers per hour) but most of the kite manufacturers you look at list knots as there primary measure of wind speed for their kites - should I start using knots?
kph and mph are both speeds that are measured by distance traveled over a period of time - 1 hour. So if you are travelling along the ground they are an accurate measure of speed.
Knots are a relative speed - they are not dependent on distance traveled and are mainly used for measuring the speed of ships and aircraft, who's speed is greatly effected by fluid factors (wind and water). If I travel at 1 nautical mile per hour in the sea I may not have traveled 1 nautical mile. The tide may be with me or against me. If the tide is with me I will travel further, if it is against me I will not travel as far. The same with aircraft. If I have a following wind I will travel faster, a head wind will make me travel slower.
So from now on I think I am going to start using knots as my preferred measure of wind speed and kite wind range and will change the units on my anemometer.