Hmm, slightly disappointed with these.
I'll speak of Drar's Wardens Battlehost first.

Drar's Hunters have Ambusher special rule, so you can easily get them behind enemy lines or in a flanking position.

However for the Ranger & Iron Guard formations of the Battlehost to benefit of the 2 'Within 12" of Drar' rule... you have to be close enough to the ambushing formation!

And the special rules of the formation were made specifically one for the Iron Guards (Always pass 'At the Double' test) which means you need to have a hero in that formation to use that rule, and they have to be near Drar's formation which maybe not always be possible if you want to ambush! Thus the times you want to At the double! you cannot unless you sacrifice the Ambusher rule to stick close to your other formations,... ARGH

and the other special rule is that you can do a full move and still shoot, while within 12" of Drar.. of course drar's hunters will always benefit of this but other ranger formations... again they need to catch up to Drar's ambushing position or sacrifice drar's ambushing to stay with other formations.

At least there is still a very tiny bonus: All the formations of the battle host (Up to 4 Formations of Rangers and 2 of Iron Guards, plus Drar's Hunters) are upgraded to M6 and Patherfinders (Master).

But that's the limit of the bonus, for which you pay as much as a formation's captain.

I'll post about Dain's Host when I feel like writing more but I'll give my opinion right now: Good for 2500+ point games, below that its hard to fit in all the requirements as the Common Formations/Companies of a Battle Host do not count for the Decrees, so even with 3 common formations of 3 companies being the minimum requirement in the Host, you have to field in more common formations to take any other rare (Battle Host allows 1 King champ and up to 2 Khazad formations) like Ballistaes and Wardens.