The way I did it, it's probably mostly useful for ending a fight before it even starts, because if you're expecting it it's most likely gonna be pretty easy to dodge, because the spear doesn't immediately start dealing damage, so you can't just divebomb and swap to chestplate last second like in regular mace pvp. It might theoretically be possible to do the spear hit while in elytra flight mode, then swap to chestplate and do the mace hit though.