I have a stainless captured guide rod in my SD9. I put it there because that's the way I wanted it. I could find nothing about the original plastic one that I could criticize except that it just wasn't what I wanted. I'm sure that if S&W engineers thought that the SD needed a steel rod, they would have given it one. But, to me, there is a warm and fuzzy feeling knowing that there is a steel one in my gun. No other reason is needed.