Not necessarily. It works on both phases, and it depends on your time and positioning when the skill activates. Battles don't tend to start until Turn 2.
Pretty sure going out of your way to get expensive fodder and forgoing any kind of buffs (in this case convenient +6 all stats)that need to be applied through hone/fortify just to counter an easy to kill character isnt worth it
Maybe I'm playing AR and Aversa's in the back, and the unit I want to kill can only be killed by Even Spd Wave BDSM Eirika. In that case it's worth foddering a Karla in my opinion.