Sword breaker offhand weapon or weapon kit

Would like to suggest sword breakers as either an offhand weapon, or a weapon kit that can be added to some weapons.
Swordbreakers would be used to parry/block attacks, and, when successful, cause additional damage/decay/weardown to the weapon that was blocked.

It wouldnt work as a weapon kit, although it would be interesting as a offhand weapon. It would be extremely tricky to balance. I would almost say that it would be impossible to. If it does enough durability damage to be useful it would most likely be the only thing people use or if its too weak no one would use it.