I am glad I magnetized my Terradons, because like you said, the Javelin option actually got better due to the new summoning rules. Terradons make a great harassment unit. They do enough damage so the enemy cannot ignore them, and when you summon them he knows that he has to attack them rather quickly or face the possibility of them dropping mortal wounds on his units. That causes some enemies to make bad decisions, stuff like attacking them with way more stuff than necessary, moving important units out of position to attack them, or wasting other resources (like spells) on them. And then if you do attack with them they are glass cannons and not quite as good as Rippers, but not that bad either.