Edit: 'like what your conversion Sletchman! I was just wondering in which category to put it, hence the new one.
Raaaah, damn 8-ball!

Well, since it was kind of urgent I did it myself. Here's what I came up with, if anyone's interested. There was so many reasons the panzerfaust needed to be a weapon I gave up the idea of making it a "Good". But since there also were too many specificities concerning that weapon, and others like it, I decided to simply create a new weapon category, with its own rules.
Unarmed WeaponsUnarmed Weapons deal with all weapons that don't work by themselves, but upgrade or otherwise modify the unarmed fighting capabilities of the character. Hence, fighting with such a weapon is similar to fighting unarmed whenever the question arises. Further, since these weapons are usually gloves, knee pads, or other body accessories, they generally can't be disarmed.
Panzerfaust: This iron gauntlet is an eisenor specialty, whose warriors use to parry incoming strikes and block their enemy's weapon.
Dmg +1; Crit 20; Qualities:
pummeling; SZ/Hands M/2h; Const Hard 2; Comp 15W; Weight 12 lbs; Era Feudal; Cost 20s
And a few unarmed combat feats:
Panzerfaust BasicsAn iron hand ... in an iron glove!
Prerequisites: Parry maneuver
Benefit: Any panzerfaust you wield gains
guard +2. Further, you gain a stance.
Panzerhaltung (Stance): You gain a Reflex save bonus equal to your Strength bonus. You may not move while in this stance, though you may still take 5 ft. steps.
Panzerfaust MasteryYour panzerfaust is litteraly an extension of your arm.
Prerequisites: Panzerfaust Basics
Benefit: You may use shield tricks with a panzerfaust you wield. Further, you gain a grapple advantage.
Crush (Panzerfaust Grapple Advantage): Your target suffers a battered limb critical injury
(FC 207). This advantage may be used up to once per enemy per combat.
Panzerfaust SupremacyYour grip can break steel.
Prerequisites: Panzerfaust Mastery
Benefit: Any panzerfaust you wield gains
grasp (FC ??). Further, you gain a trick.
Steel Breaker (Panzerfaust Parry Trick): If you succeed, you also inflict your unarmed damage to the weapon (or the attacker, if unarmed) who tried to harm you.