Shadow Weapon

[Bladelock]

A while ago I came up with a crazy idea to use shadow weapon in a campaign. What could be used with the spell seems straight forward to me and everyone at the table, but never got a chance to use it. Have a new GM that feels almost no damage enhancing metamagic feats can be used with it.

My original understanding was as follows:
Am I wrong about how I'm interpreting the spell?

Metamagic that can be used:
Dazing
Disruptive
Echoing
Ectoplasm
Heighten
Intensify
Jinxed
Merciful
Persistent
Piercing
Quicken
Sickening
Silent
Still
Tenebrous

Metamagic of note that cannot be used:
Maximize
Empower
Umbral
Shadow Grasp

Any feat that would work with a weapon that is the shape of the shadow weapon will work with the shadow weapon. Plus:
Spell based feats:
preferred spell
spell focus
greater spell focus
spell perfection
spell penetration
greater spell pentration
spell mastery
spell specialization
greater spell specialization

[Byakko]

I think the confusion stems from the fact that it seems the spell is only forming a weapon rather than being the weapon. Kind of like a temporary creation spell. Naturally, the other way of looking at it (the shadow weapon is all magic and thus affected by any applicable metamagic) is also a reasonable reading.

I'd probably go with the latter reading personally, but expect table variation, imho.