Howdy Tombstone, and welcome!
Midiman pretty much hit it square on the head.
The polymer guide rod is fine, and the metal rod is also fine.
The polymer one is apt to pick up a selection of dings, scratches, and contusions over it's lifetime, but they don't seem to fail!
Metal rods ARE stronger, but functionally aren't necessary. They are, however, easier to reinstall than plastic ones, and are standard equipment on a P-3AT. Kel-Tec sells them for the P-32.
The drawback is that they'll likely wear the guide rod insert in the front of the slide, which is no real big deal for it's easily replaced.
It's up to the user, I guess! Either one works great.
Flyer