I almost exclusively play decks, and all of my decks have a heavy threat-reduction element to them. So I've tried most of the threat control options that the game has to offer. FotV has become my favorite of the bunch for many reasons. If you are threat goalie, this should be one of the tools in your toolbox.
The ability to recycle FotV is one of the main advantages it has over the Event threat reducers. Using Sneak Attack with Gandalf already? Add 1 FotV and 3 Erebor Hammersmith and you now have nearly unlimited uses of FotV. There are other recursion options as well. Not to mention, it's , and is a great complement to core Gandalf for non- decks.
Efficiency is not obvious at first blush. Most threat-reduction comes at some fixed amount. The value on FotV is always at least 6. But, if you're at 49 and take 11 threat increase? Its value is significantly more than before. If you're planning on using FotV around skipping questing, Wandering Took, Heirs of Earendil, Frodo Baggins, and more, this becomes much more than simple threat control, it becomes a threat editing tool. If you're running threat-goalie with Song of Eärendil, you only need to cast this on yourself as well, and it becomes incredibly easy to hover at 49 to maximize the benefit from this card as well.
Lastly, crazy threat reduction decks can prevent players from using Valour effects. I've always felt that situation falls into the 'happy problem' spectrum, but it's worth mentioning that FotV lets your allies use Valour actions without having to worry about threating-out. It's an easy to use card. You don't need to cast it at any specific time. It's easy to cast cost-wise. And by the time you need it, you're usually at the stage where you have extra resources. The peace of mind it offers is hard to explain until you've used it.
Unfortunately, it is not a great threat reduction tool if your goal is to stay below engagement costs. Or if you're aiming for secrecy or something like that. It's not for every deck. But, when putting your threat-editing suite together, I strongly suggest you give this a playtest or two.