Bitterman:
Well, apart from the 2D6 + 2 str 7 impact hits.
Baggronor
But it only gets those impact hits if it charges. And to all intents and purposes, it is only possible for it to charge if your opponent lets it. You have to line it up ready for a charge, then your opponent gets a turn of movement in which they can simply step 2" out of the way (or feed it a 30 point unit of Gnoblars, or charge it themselves), and only then do you get to charge, if they don't do that - perhaps if they're already tarpitted by another unit. Every other unit in the game (AFAIK?) is able to pivot up to 45 degrees before charging; the Iron Daemon can't, and nothing costing 300+ points is ever going to be worth that restriction IMO.
Of course - even if it does get to charge (whether via an opponent's mistake or your own good manouevring) and even if it does then win the combat, it can't chase down a fleeing opponent... uh oh. And should the enemy not flee, it's back to 3 S3 attacks against anything it can't Thunderstomp.
So in damage output terms, it is
only any good
if it gets to charge (which it finds more difficult to do than any other unit in the game), and
if it either wipes out the opponent with impact hits or
if it has another friendly unit in the combat that is able to pursue on its behalf (though such a unit is likely to be much less tough than itself so may give away CR and make you more likely to lose the combat!), and/or
if the enemy unit you're interested in killing is small enough to Thunderstomp. I'm not saying that makes it completely useless... just that all those
ifs make it not worth the points IMO.
And the fact it can tarpit pretty much any unit in the game, even Iron Guts/Maneaters. Against Ogres, that's pretty useful.
If you take IDs, take 2-3 and a Destroyer; that way its much harder to avoid them.
True, it's an awesome tarpit. No arguments there. I'm just curious why an opponent would ever bother getting into combat with it with a unit they didn't want tarpitted, knowing how easy it is to avoid and how good it is as a tarpit.
You may be right that taking multiples is the best way of mitigating that. After all, the enemy can easily sidestep 2" to avoid one Iron Daemon; but if that takes it into the charge line of another, or closer to a Destroyer, then yes - it's much easier for at least one of them to be able to charge. The flaw I see in that plan is that you're by now spending somewhere between 1000 and 1300 points to compensate for a unit not being worth 300ish points (...though the Destroyer is always going to be good value, granted). Can it be made to work? Yes, I'm sure it can. Are there better options in our list to spend 1000 points on? For certain.
Ultimately, that's what it comes down to. Six Bull Centaurs will be dramatically better in almost every situation, than an Iron Daemon Skullcrusher. The only thing they don't have is high Toughness. A Destroyer is also dramatically better, though access to it is more limited (can't get two in 2000 or 2400 points). K'daai are possibly also better, though admittedly they are in some ways more fragile (it's hard to directly compare). The way I see it, the Iron Daemon is basically the fourth best choice for that role in a list where you don't get to take many units... worth taking for the awesome model if you're playing a big game for fun, but not close to competitive.