Two things to remember.

First Jinettes get four shots before running empty, and these are best used on elite armored troops.

Second, Javelins can suck, but they can also be deadly. They are quite effective when trying to break down a high valor elite armored unit holding a bridge or hole in a castle. Place them on Hold Form in deep formation and order them right up behind your good inf, then manually order them to toss their pointies at the toughest enemy unit.

Javelins can also work well in the open skirmishing against enemy inf. Just don't let them try to melee. They can kill some or at the very least, exhaust an enemy unit trying to chase them down.

ichi