I'm not sure if the stiffness of the wire matters at all, but I'm guessing that the galvanized wire will be more prone to bending in unwanted ways. Again, not sure f that matters at all, but it's the first thing that came to my mind.
And I believe
@bullet20dc is right when it comes to the hardware missing. The swivel, etc. are critical from what I understand, to prevent nasty line twist problems.
On another note, some people are starting to use this rig for punching grass beds and other dense weeds with great success.