I only could find the following official information (this is an official text from the old EU-Server forum after the last Galaxia Update posted by a CM there):
(taken from the old EU-Server forum)
The Block Chance rate has been changed as well. Currently, the Block Chance rate is displayed as a value with the name "absolute def rate". In addition to this, there is now a new attribute: Block Chance. Both of them can be viewed in the new "Unique" attribute category in the character window. In order to check your Block Chance rate in % (vs. an enemy of your level), simply hover your mouse cursor over "def rate".
• Absolute def rate (Block Chance rate): First, you'll need a base value, since all percentage-based Block Chance rate bonuses are relative. This means that nothing can be increased without a base value to go on. This base value can be acquired through equipment that can be used to block. Several shields and katars already have received the attribute "def rate".
• Block Chance: This is a percentage by which the damage you take from a blocked hit is reduced. If you have 50% Block Chance for example, you will only take half of the damage you would usually take. This also includes elemental damage!
Against enemies of the same level, a Block Chance rate of 40% can be achieved. The damage received from a blocked hit can be reduced by up to 99%, meaning it can be mitigated almost entirely. Thus, "absolute def rate" and Block Chance remain very valuable attributes that can have a tremendous effect on combat.
I can't guarantee this is completely right, but the only reference I could find. Nowhere is written that this stat is only for knights, but if someone knows more, please correct this info.
How useful this stat is for any class I can't say.
Edit: Also, I see that this stat you're speaking about is the "SoulCraft" effect.
As far as I know, Soulcraft effects are completely random and not bound to any class. So if it's right that this stat is only for knights, it's just a useless stat for your class you got by unsealing this bracelet.
But I'm not 100% sure regarding this "only for knights" thing.
Maybe some other players hanging around here have more experience with this stat and can clarify this?
Edited by VModPopcorn, 29 September 2014 - 12:26 PM.