Compact
LOL, my first thought was compact as well. You get full size scissors that way and tweezers. Thats the only things Id miss if I only had a spirit and no SAK at all.
I know I am taking a slight side trek here but how about leatherman micra?I have Spirit S and I chose to buy leatherman micra to accompany it. It has worked wonders with very little redundancy. Spirit S has the serrated blade instead of the scissors, Micra has top tier scissors better then Spirit X's scissors. Micra also provides you with mini flat head screw driver, tooth pic and a ruler. Small but important implements Spirit S lacks.