A 1-for-1 cost-to-Willpower is always good and since nowadays there are a lot of treacheries that remove character from the quest it can always be useful. It's make the best use of where you can use to boost other stats like with Herugrim, Golden Shield, Fair and Perilous but generally amazing. Of course it can be paired with a Westfold Horse-breeder to fetch it.
Attachment. Cost: 1.
Attach to a hero, or to Éowyn. Restricted.
Attached character gets +1 .
Response: After attached character is removed from the quest, exhaust Windfola to commit attached hero to the quest.
...the great grey steed Windfola made little of the burden; for Dernhelm was less in weight than many men, though lithe and well-knit in frame. The Return of the King
A Storm on Cobas Haven #116. Spirit.