Thank you, Taran!
Assuming you are right, in which Situations would you choose for Harry's Duster to act as Armor? The block seems to be the by far better choice.
A single-
attack Exchange block is great for protecting against big hits but is a waste against many small attacks since, even if it successfully blocks an attack, it goes away in the next exchange unless you reduce its effect to put in extra shifts of duration. Of course, if you choose to make your (Block 6) shield into a (Block 5; 2 exchange) shield, an attack of 6 will get reduced by 5 but the attack still overcomes the block and will immediately destroy it, regardless of duration. So, the longer the duration you want, the less powerful your protection and the more likely it will be overcome. The higher your protection, the more careful you'll be to use it because you don't want to waste it. (Enchanted items don't recover daily, they are recovered per session)
On the other hand, an armour 2 enchanted item that lasts for 3 rounds (4 shifts halved for armour 2 +2 more shifts for duration), will last for all three exchanges and will reduce damage from all attacks and is, obviously, much more useful against many attacks from multiple enemies. Ideally, you'd want both!
It's also very useful if you have some kind of secondary dodging skill and you often find yourself only taking small bits of damage.
Made some edits.
IMO, most wizards go with a high-value block and save it for a big hit or for being surprised. If I feel I'm going to get hit a lot, I'll spend an exchange to cast some kind of defensive spell rather than have an armour enchanted item. That said, if you are playing solo, and expect to get attacked alot, having armour is of value. But, usually, its more efficient to buy mundane armour than to waste valuable spellcasting/ Enchanted Item resources on it.