It's probably not going to be useful the majority of the time. Off the top of my head, I can't think of any scenario where there's just a big mob of enemies except one part where killing a bunch of them goes against your best interests.
Chiming in a little late here, but I'm going to have to disagree with Rynjin. I have a player in my group who runs a Fighter/Barbarian/Shadow Dancer with the Whirlwind build and it has been quite effective. Anytime there's multiple enemeis its been a very successful attack feat, especially when its a mob of badguys with low AC.
Chiming in a little late here, but I'm going to have to disagree with Rynjin. I have a player in my group who runs a Fighter/Barbarian/Shadow Dancer with the Whirlwind build and it has been quite effective. Anytime there's multiple enemeis its been a very successful attack feat, especially when its a mob of badguys with low AC.
So, I don't know what awaits in book 5 or 6, but so far, I don't see any places (or rather, very few, and none memorable) in which there are mobs of enemies with low AC.
Almost every encounter I remember has been with boss type enemies.
The cultists at the beginning of book 4 comes to mind... especially if they all mob at once (as is only reasonable). But yeah, maybe once or twice an adventure does this really come up... book 3 is probably the most frequent with a couple werewolf fights and that wonderful skeleton mob.
One of my players is a Scythe Fighter who specializes in Cleave and Cleaving Finish, and he has found (in conjunction with Lunge) these feats to be incredibly useful, though not in every encounter. We're halfway through book 3, so I'd say that a Whirlwind-style fighter, given the right weapon choices, would be very useful. Also, all of the Prerequisite feats for it are pretty good in of themselves, so you're not wasting anything by building towards that. (Mobility arguably being the weakest of the four)
Not including book 1 since it would be impossible to have that Feat by then, but in Book 2, the Schloss, by its very map design, funnels enemies at whatever PC walks into the room first (rust monsters, fungi, wights, vargoulles)
In Book 3, you've got a least a couple encounters with multiple werewolves (who usually flank like real wolves) as well as the hordes of undead that are in Feldgrau.
In Book 4, you've got the cultists, skum, mi-go...
So I can think of quite a few places where trading your iterative attacks for a swing at every creature is often the better choice, at least so far.