I think the most interesting candidates for this card are investigators who also have access to the Mystic class.
As of the Scarlet Keys, this means : Carolyn Fern, Sister Mary, Lily Chen, Amina Zidane (remember, Vambrace is a charm), and to a lesser degree, mystic Carson Sinclair and Zoey Samaras. Unfortunately just out of reach for Diana Stanley...
Low-level mystic events offer awesome possibilities for dealing with the encounter deck's treacheries (Deny Existence and Ward of Protection are staples for a reason). You can now redirect a dangerous card drawn by a teammate to yourself if you can deal with it (it has probably happened to some/most of you that your friend drew an Ancient Evils while you were the one holding the cancel...)
Compare the 2 xp cost to upgrade to Ward of Protection (2) VS the 3 xp cost of this accessory, that grants a similar benefit to multiple cards, on top of good soak and a bonus to ALL skills against revelation effects. This brings these characters' average-to-good Willpower (except Carson Sinclair...) to interesting levels, and shores up their Agility/Intellect defenses as well.
Of course, Ward of Protection (2) has the advantage that it can be used at any location, while the Vambrace encourages you to stick with your fellow investigators.
Lastly, as Guardians / Mystics, most of these characters can be built as enemy-managers, and the Vambrace can redirect an enemy to yourself, potentially saving you an "engage" action and/or preventing the sudden appearance of an enemy on your teammate from messing up your team's activation order.