OK, well as an "Expert" why not just buy the stainless system and forget it? It seems to me that you eluded to the possibility tht the stainless aftermarket may be superior. Is it, or isn't it? THAT, is the question!
I put "expert" in quotes because I am not a gun designer, engineer, or gunsmith, but due to the luck of the draw, I probably have had more experience in dealing with defective factory Shield RSAs than anyone else on this forum. You can read my well-documented story in this forum thread:
http://smith-wessonforum.com/smith-wesson-m-p-pistols/432397-shield-rsa-one-more-time.html
Many of the responses to my original post in that thread were from Shield owners praising the effectiveness and reliability of the factory RSA. I had no reason to doubt them. The SS guide rod was mentioned at that time, but I did not consider getting it for several reasons:
1. When I paid good money for a new Shield, I did not expect to open the box and find a bent-at-the-factory recoil spring retainer disc. I expected one in perfect condition, and when I found it damaged, I expected Smith and Wesson to send me one quickly (didn't happen) at no charge (did happen). I am way too cheap to pay for a part that S&W would send me for free.
2. Because of others' replies to my post, I expected that a proper S&W RSA would work reliably for a long time. Although the Shield was new to me, I felt I could trust the responses of the forum's veteran Shield owners.
3. The S&W Shield two-spring RSA is nearly identical in design to the totally reliable one in my SIG P320. My SIG has 3500 rounds through it with only one FTE, and it is still going strong. Thus I saw nothing inherently bad about a two-spring RSA.
4. To get an SS guide rod RSA, you had to donate your factory RSA so they could take it apart and put the big spring on their version. If any problems arose, I would not have had an RSA, because at that time, S&W didn't have any either.
5. S&W engineers designed the Shield's RSA the way they did for a reason. The problems with the factory RSA were not with the design, but with the execution. Numbers of them were either manufactured poorly (the fly-apart models), or installed incorrectly at the factory (the bent-disc models). Well-made examples worked just fine, according to forum members. I did not know if the very different one-spring design offered by SS guide rods would be an improvement over the factory design, or an effective long-term solution. Neither did anyone else, because there were no long-term users at that time. I did not want to pay to be a beta tester. (Did I mention I am cheap?)
It looks like you and the OP have decided to go with the one-spring replacement model. I hope that it works for you guys, and I applaud your willingness to be early adopters. Post a report after you have some experience with it, because I'm sure there are many forum members who will be interested in how well it performs.