two ASF units/models fighting each other swing simultaneously, but most importantly you negate the enemies rerolls to hit if you both have ASF.
By your logic then sunny, a hero in the second rank would get extra attacks from red fury or get more than 10 attacks since it's an army ability, none of those have merrit since it doesn't say you can attack with more attacks if you have red fury. There is nothing that allows more than 1 attack from infantry support attacks in warhammer, if it did, it would specifically say so in it's rules, which PF does not. Same with ghoul kings, they lose their poison when they take an ogre blade, even though it's a selection in an army book vs the BRB, it doesn't say it keeps it's poison so therefore it loses it when it takes a magic weapon, the same applies for PF, it doesn't say they ignore the support attacks rule, so therefore it doesn't.
I like cohorts, they are movement 6 and the krox can add some punch, especially against weak troops like elf spearmen and most of the skaven infantry.