I think you could also get away with leaving it more generic like this example:
@Override
public void onArmorTick(ItemStack stack, World world, PlayerEntity player) {
if(
!player.getItemStackFromSlot(EquipmentSlotType.HEAD).isEmpty() &&
!player.getItemStackFromSlot(EquipmentSlotType.CHEST).isEmpty() &&
!player.getItemStackFromSlot(EquipmentSlotType.LEGS).isEmpty() &&
!player.getItemStackFromSlot(EquipmentSlotType.FEET).isEmpty()
)
{
player.addPotionEffect(new EffectInstance(Effects.INVISIBILITY));
}
}
This way if you create more armors you don't have to write new conditions to check more items. Although, yours is better if you want to guarantee that all armor pieces match the suit in their slots.