GryMor has a point, but I find the roll-replacing ability of most defensive enchanted items to be equally useful as the aspect creation. If I roll abysmally and activate my defensive item, a +6 to a roll is no small thing, but when I just rolled -3, it's not a huge help. I would much rather have a +9 as my defense roll or Armor:4 in that situation.
You can spend tags on rerolls, too. So if your base defence skill is 6, then a triple-tag provides (on average) the same defensive bonus as a 9-shift block when you roll -3 and a better one when you roll -1 or better.
Plus it lets you save tags for later, if you don't need them all. And it has applications beyond simple defence. And you can boost your defence further with FP and more tags when using it.
So the maneuver item is, when given to a combat character, generally better than the block item. The defence roll it provides only becomes worse on average when the character using it has a skill of 2 or less, and even then it has significant advantages over the block item.
And of course, even if it was weaker, letting it exist would make crafters stronger.
Actually, is it just me, or does the "use it again for 1 mental stress" ability of Crafting make it objectively more powerful than Evocation?
No. As GryMor said, crafters must choose between accuracy and damage. Plus crafters have to choose their effects in advance, and they're really gear-dependent.
Worth mentioning that evokers can't blow control rolls on their main spells either, what with Rotes and all.
Upon further thought, someone with Thaumaturgy and nothing else but Refinements devoted towards Crafting and a thematic specialty is probably one of the deadliest characters it's possible to play.
Yeah, it's one of them.