So that's 8 times a +4 to the roll? I'd seriously question that. If the enchanted items create aspects, and those aspects are applicable to pretty much everything, I'd veto it entirely. Make different items that have situational applications and all is good. If you can shove the game into a direction so you can use all of them, kudos to you.
Then there is another issue. Maneuver spells usually require an action to be used. I could see an item every now and again that allows you to simply use the aspect it would create, if it makes sense, but I would not let players create enchanted items that only do this. They should be the exception, not the rule.
And if you have to spend an action to create aspects, other people can use their action to remove the aspect or at least remove your tag on it. Especially if you create 2 aspects simultaneously, which means each aspect can be removed with significantly less effort than if it was only one. After that, it's not going to be nearly as powerful.
Two things keep coming to mind with the discussion about using Enchanted Items to provide bonuses.
The first, (which people seem to be overlooking) is that the RAW allows an Enchanted Item to store/cast one single spell. *Yes, a Warden Sword is an Enchanted Item with two different functions but that is a special case. Depending on the GM and table choose to interpret or allow, this means the Enchanted Item can only cast one spell which either could only do the same Maneuver, or it might be allowed to perform different, similar Maneuvers. In other words the Enchanted Item couldn't be used to perform a Maneuver to knock over a case of ball bearings to create a Temporary Aspect: Unsteady Footing and then at some other point do a completely different Maneuver to create a fog cloud for a Temporary Aspect: Obscuring Mists.
The second is that Maneuvers to create Aspects are either opposed rolls (much like an attack roll) or against the environment. In a number of cases, a difficulty of Good (+3) will allow the creation of a Fragile Temporary Aspect against the environment however that isn't true in all cases. Using the example above of creating a fog cloud, in an area with plenty of water/moisture and cool air that could quite easily be only a Good (+3) environmental difficulty. However, trying to create the same sort of fog cloud at high noon in Camp Kaboom, New Mexico... That would likely a Fantastic (+6) or greater difficulty.
The variations in difficulty depending on circumstances are important because what the Enchanted Item can accomplish (shifts of difficulty) and number of uses is set at the item of item creation or the appropriate milestones.
In the example given by InFerrumVeritas, the +3 item 3x per session would allow Temporary Aspect creation via Maneuvers three times per session without causing Mental Stress, assuming the environmental or opposed difficulty was only Good (+3) or less. However, if the difficulty for any of the attempts was Great (+4) or better, the Maneuver would fail, the attempt used up, no Temporary Aspect created, and using the Enchanted Item to maneuver would require the character to use an Action.
If the players are creative, then they might come up with spells for a maneuver which is fairly broad, allowing more frequent application when creating Temporary Aspects, but in general I would consider using an Enchanted Item like this inefficient or wasteful.
-Cheers