First, you have to memorize most of the ruleset, which is easier than it sounds but still not easy. Then look at what each new Power or Stunt offers and compare it to what's available. If it's significantly better or worse, it's not balanced.
(Either that or look things up obsessively.)
I usually do the latter until I reach the former, so we pretty much do the same, only to reach different conclusions.
If that fails, break it down into number of shifts and look at how frequently those shifts can be used. See how many stunts it's worth. Then see if buying the effect with stunts would be optimal. Compare to other Powers and Stunts from there.
I usually try to break bigger powers down into 1 shift powers to help me understand them. It is not always possible, and often enough, a 3 refresh power is worth more than 3 1 refresh powers. Evocation for example gives you significantly more than Channeling + Refinement. Channeling on the other hand is exactly worth 2 refinements, 1 for the element, 1 for the items.
You should really post a proper writeup for this Power.
How does that sound:
Bag of Tricks [-1]
Description:You are not a wizard (or are but unable or unwilling to create magical items), but know someone who can provide you with a few magical trinkets for you to use.
Skills affected: Contacts
Effects:Enchanted items:You gain 4 enchanted items, each at a power equal to your contacts skill. These enchanted items can each store one action that can usually be stored in an enchanted item. Bonuses to crafting never apply to these items. Each item can only be used once per session, no exceptions. Using any of these items counts as an action in a conflict. You must decide the spell embedded into the items when taking the power. You can switch out these spells at any milestone (if you can get to your source at that particular moment).
Bigger bag [-1]
Description: You have a few more items in your bag of tricks.
Musts: You must have the
Bag of Tricks power above.
Effects: More trinkets: You gain 4 additional enchanted items.
First, this limits the power to 8 items for 2 refresh, more would definitely be pushing it. Second, it should be absolutely clear, that the power of those items is limited to the value of the skill. If anything is left unclear,
Now there can be different versions for multiple skills:
Bag of Tricks [-1]
Description:You know where to buy a few magical trinkets for you to use.
Skills affected: Ressources
Bag of Tricks [-1]
Description:You know where you can steal a few magical trinkets for you to use.
Skills affected: Burglary
And so on.
The problem with what you have here is that it offers the buy-in of Crafting for free. Making enchanted items costs 1 Refresh, then you buy enchanted items 4 at a time for 1 Refresh each. That's how Ritual (Crafting) works.
Like I said before, I see a value in crafting over only enchanted items that makes up for the 1 refresh it costs more.
This lets you bypass that buy-in, so that you can just buy items. This is inferior for people with large amounts of Refresh that they wish to use on items, but superior for everyone else. Also, it lets you use whatever skill you please for free. Can't ignore that.
Yes, that's precisely the point. It is meant for a mortal that wants a little edge, nothing more. If it makes you feel better, I can add a requirement, that the character may not take up any other powers along with this one, so it really only fits this little niche.
I don't see the part about using another skill as not that important here, since it is a "power", not a stunt, they can be a bit more flexible. I said it somewhere before, if it fits a character, I would let a player take evocation with 3 entirely different skills, as long as I can see that it is not intended to be for minmax purposes only, but rather because it fits the character better.
Being able to prepare four one-use stunts is pretty awesome, especially since enchanted items are less limited than stunts. I'd pick a coat that provides a (Contacts) block 4 (or 7 depending on how you read) times/session over any defensive stunt if my Athletics was low and my Contacts was peaked.
Sure, you can do that, you would get 4 contacts blocks (lets even make them work reactively) for 1 refresh. You could also take a stunt that lets you use contacts as your goto dodge skill (well... ok, contacts might be a bit iffy here, I admit, but lets stay with it for now). With the stunt you can use your contacts skill indefinitely, and you can boost it with aspects if need be. A block from an enchanted item is always at a fixed value.
Also, you can get supernatural toughness with the right catch for 1 refresh, which may even be better then stunt and items combined. And remember that items are always susceptible to the old "take them away" tactic, while stunts are not.
How do you get to 7 uses?
If I were writing this, I'd make a Contacts or Resources stunt that lets you obtain enchanted items with a roll at a difficulty set by the GM. Unreliability seems appropriate for an ability like this.
I would always treat this as a power, since the character concept is based on the supernatural. And if the skill is high enough, there should be no problem in pretty much always getting the desired item. Randomness is well and good, but not if a characters high concept is depending on it.
If you really want to, you can play out the "reload" of the items, when the character is getting fresh trinkets, and his wizard friend doesn't exactly have in stock what he is demanding. Can also be a great source for compels ("You know, I couldn't finish that flash stick I promised you, but try this here, it should more than make up for it." And you hand the character a trinket of unknown properties and the player a fate point. Somehow that wizard looks like Q in my mind right now.). Actually, it is a great source for compels, which I know we have different opinions about, but I really consider this a good thing.
How would you feel about a wizard + adventurer tag team, where the wizard is mainly creating enchanted items for the adventurer to use? In that scenario, the entire burden of refresh would sit on the wizards shoulders, while the adventurer could still benefit from the enchanted items. My power simply moves the wizard into the role of an NPC and shifts the costs to the actual character.