"Let me handle this!" in asset form. I think it's pretty good for the right characters that are aiming to tank for their team.
Most guardians have good agility and will so they're moderately if not good at defending against the encounter deck. The only downside is that they have low sanity...but this provides some protection on that front.
2 health and 2 sanity soak for 2 resource is pretty reasonable. Accessory isn't particularly in high demand for guardians, the immediate comparison for me would be Holy Rosary. Both cost 2 and give 2 sanity soak, but this also gives 2 health soak, let's you take other players encounters and gives +1 to all skills instead of just will. On the flip side, it costs 1 more exp, you can't actively use the willpower outside of mythos, and you don't have a chance of getting bless tokens. Seems like a fair trade off.
You could probably use this in a variety of investigators but someone like Tommy, Zoey, Roland, Carolyn or Mark would probably be most interested in it. Zoey can get resources for engaging enemies, Roland can kill enemies for his passive, mark gets stuff for wounding his assets and Carolyn can heal herself up easily.