After reading a rules question on another website discussing whether Grotsnik could give Dreadnoughts Battle wagons, etc cybork bodies, I realized that many Chaos Space Marine and Chaos Daemon players are using the Daemon rule incorrectly on Chaos Daemon Engines.
The argument came up that Grotsnik could not give the Ork vehicles and walkers cybork bodies, because invulnerable saves can only be taken against wounds, not damage. Therefore under that reasoning, The 5+ invul save that the daemon rule gives, can not be taken by daemon engines, because they take damage not wounds.
A Dread Knight that somehow gets an invulnerable save could use it however because it has a toughness value, even though I think it should be classified as an open topped walker, and be given armour values instead.
Since more than 70% of the armies you see in tournaments, or even in general wargaming come from the various Loyalist Space marine codexes, they normally either get fearless or ATSKNF, and so are immune to the Daemons fear rule. The only reason for them to have the Daemon rules really is to make it easier for Grey Knights to hurt them.
This certainly makes it a lot harder to use the Helldrake. If it takes a jink cover save, then it can not use its Bale Flamer in the next turn, as it can only make snap shot if it Jinks. They are then either more vulnerable to enemy attacks, or less effective in hurting the enemy. Now I realise why they are only 170 points each, they only have one ranges weapon, and their vector strike. This makes bale flamers less attractive an upgrade than I thought they were.