I think Galloway has revised their SD guide rods to solve the occasional problem of damage to SD frames -- but if you buy one off the internet from anybody other than Galloway directly, you have no idea if you are getting new old stock (e.g., the earlier version).
I like metal guide rods -- I put a stainless one in a Sig-Sauer, and tried the Galloway in one of my SD pistols. But now I am back to the factory plastic version. I think it works fine. I am dubious about the need for metal guide rod in the SD. The SD is a great value for the money, and adding a $30 gizmo raises cost without adding much value. That said, I think someone can add the new version of the Galloway with less risk of damaging their SD frame than was the case before members of this forum found the problem and engaged Galloway to fix it (which they graciously did).
I hate to chime in at all -- because something like a metal guide rod is like an engraved zombie insignia on the slide cover -- if you really want it, do it, its your pistol and its supposed to be fun, so who am I to criticize? But, for what its worth, I am an inveterate tinkerer with pistols (in the past: Apex parts, new sights and grips, although never lighter spring kits) and I am foregoing adding an all-metal guide rod to my very reliable, accurate, $279 SD9.
