The Spwn-kin rule says that Krox "are always placed with in the second rank," unless enough skinks get killed and your unable to reform to make a thinner unit, then they move to the front. I like to run my, usually two, Skrox units with 28 skinks, musician, standard and 3 krox. 6x3x6x6x6x4.No champs, they stink in combat any way and I dont want to give any characters in my opponents unit a chance to miss some GW lovin'. I love the speed and surviveablity of these guys. Yes skinks get mowed down rapidly but the krox are all but certain to kill a few back. I like to set tem up opposite of knight units and on flanks.
Javelins are 'quick to fire.' That means you can always stand and shoot (at any distance) and can move and shoot. You cannot march and shoot with them though.