Using Multiple Enchanted Items At Once

[Tedronai]

I like the idea of simply using declarations to model this, then compelling those aspects if the player tries to use the item again.

To me, this sounds like the best approach.

[Orladdin]

I'd suggest the rules are already there...just make a declaration.  "I'm using two charges!"  Tag it for your +2 and mark two off.  Using more than two should probably remain dependent on how the GM / table likes to use / stack declarations and aspects.

UmbraLux's suggested case, above, using a second use of the item as the cost for making the declaration (rather than a roll or FP which is usually necessary) is perfectly costed, imho, and a simple and elegant way of handling this.  If you wanted to use the rest of the rings as well, I'd probably allow the player to make two declarations: "I Use Two!" and "I Use The Rest!" and cost those declarations accordingly for one or two +2 tags, respectively.

I like the idea of simply using declarations to model this, then compelling those aspects if the player tries to use the item again.

You wouldn't even need to use compels if you consider the cost of making those declarations to be crossing off extra uses.  Then there's already rules for additional item uses.

[InFerrumVeritas]

I've got a problem with the "I Use Two!" scenario though.  As, technically, I'm always better off using this declaration and putting extra slots into frequency instead of power (since it's giving me a +2 as opposed to +1 and is more versatile).  I wouldn't allow that. 

[Tedronai]

You wouldn't even need to use compels if you consider the cost of making those declarations to be crossing off extra uses.  Then there's already rules for additional item uses.

This sounds to me like 'simply' taking a compel on the aspect to generate the FP with which to Declare its existence.
Or perhaps accepting a point of debt to Declare the aspect, then Compelling that debt immediately to arrange the consequences that will set in once the aspect is Tagged.

[Orladdin]

I've got a problem with the "I Use Two!" scenario though.  As, technically, I'm always better off using this declaration and putting extra slots into frequency instead of power (since it's giving me a +2 as opposed to +1 and is more versatile).  I wouldn't allow that.

Oh, right.  Damn.  Good catch.  You'd need to use more than two extra uses, then; but the same idea can apply.  "I use three/four/whatever-seems-appropriate-to-the-GM!"