No, good purchase -- I have the same set.
You'll notice that the polarized filters have an additional bearing and ring that rotates around the bayonet that screws on to the camera. This is what you turn to adjust the polarizing angle.
Best way to adjust this is to look at the live video on your screen and turn it until you get the best results. That is subjective, of course, but usually this amounts to the most saturated colors with high dynamic range in the shadows and highlights. I'll try and shoot something tomorrow while adjusting the polarizer and post here to give an example.
Generally, a clear sky is a good benchmark. Adjust to get the deepest blue. Rotate the filter 90° and you'll see the sky washed out.
Other applications include reducing glare from reflections on water, magically seeing through into the water while overhead, etc. Google is your friend.
Don't use a polarizing filter if you don't know how to adjust it. Have it off 90° and it'll destroy your footage. Have it set right, and it makes a big difference IMO on bright, sunny days.