We have a Wizard apprentice in my game who has a Winter Court artifact, and an Aspect related to it. However, since Refresh is such a premium for spellcasters, we built it as an Enchanted Item (using his normal focus item slots) instead of an Item of Power. It is rules-legal, but plot-sketchy, thematically, because it is (plotwise) not something he "built." That said, if it is ever taken away, it would "free" those focus item slots.
So, at the end of the day, your Wizard *could* be using those Focus Item slots for other Enchanted Items, so for simple balance purposes, it would seem alright to me to make this family heirloom an Enchanted Item. Plus, it is limited in its per-day uses, but if necessary, the caster can spend a Mental Stress point to give an additional use. It is also the cheapest way to do it. Plus, the Warden swords act the exact same way (someone else built it, but for game balance reasons, it is taken as an Enchanted item instead of an Item of Power). Which would make it technically breakable.
But the "pure" plot solution would be for it to be an Item of Power. Which also means the item is not breakable. And since this is an NPC already, spending the Refresh is not necessarily a problem.
