I do not like using boots on a ladder. The arch area does cup the rung, but it also can make your foot uneven and want to slide towards the rung while you are going up and down. I like a good flat tennis shoe so I can "feel" the rung under my foot.
I have had more problems with the style of extension ladder that skips a rung where the extension locks are. How many times have you been going up or down a ladder thinking about your project and put you foot where there should be a rung and find out it is in the position of the locks and doesn't have that rung and your foot hits "air"?
Adjust the feet into the upper sideways position and let the rails of the ladder stab into the ground to help secure it if you want to keep it in place on soil. Use the rubber feet on cement.