BAREFOOT SCIENCE4 Step Multi Purpose Insoles, Full Length, Size Large

Besides the obvious, what's the difference between the full-size and the 3/4 size. What are the advantages of one or the other?

Q1. this listing says size medium. what exactly is size medium in shoe size? I wear about a 7.5 or 8 women's.

My husband is 11.5 to 12 depending on the style of shoe. Should I go with large or extra large for him?

Difference between 4 step and 7 step