I picked a SSguide rod up for my Shield 45 mostly because it worked out really good in my Shield 9 and I like one piece/single spring assemblies for simplicity. My full size M&Ps all have single spring assemblies.

There's absolutely nothing wrong with the stock spring and I'm sure S&W did their research to make sure it works with all the various bullet weights one can purchase. That said, some loads prefer heavier springs, some prefer lighter. In my Shield 9, noticeable improvement in accuracy going to the SSguiderod with the my SD ammo and reloads. For me, and I repeat for me, the bullet weight used preferred that spring weight in my firearm with me shooting it. What works for me may not work for others. It's strictly on a case by case basis. No noticeable recoil difference. Slight difference is point of impact. Don't shoot plus P, or at least those that actually perform to plus P.

Just spent most of the morning at the range tuning up a few firearms and checked out the SSguiderod in my Shield 45. Primary focus was accuracy, to include any noticeable differences in reliability and recoil. The people who build the SSguiderods test their product, so wasn't expecting any radical differences. My shield 45 loves PMC gold 185 JHPs and my reloads mimic their performance using Zero 185 JHPs. It will just eat the center out of an ICE-QT target all day long offhand at 25 yards if I do my part.

Started out running 8 rounds of PMC, with the stock spring to verify point of impact and grouping. The group is very consistent. POI may change a little if the stance/form gets lazy. As expected, 8 rounds in ~4" circle @ 25 yards offhand. Group was slightly high and to the left. Swapped to the SSguiderod, shifted my stance/hold slightly and proceeded to burn 8 rounds of PMC into the center. Great group, little/no noticeable difference in recoil. Not one hiccup. Changed up to my reloads and continued to keep ~97% of the rounds well within 4". Done deal, the SSguiderod is staying put and I'll keep the stock as a back up.

Again, this is on a case by case basis. Works for me and my particular setup. Can't say it will work for anyone else. Not worried about "beating the gun up", they're definitely not plus P rounds. Besides, it's a Shield for pete's sake not a $1500+ 1911. The LGS had a June sale on Shields. $300 + tax out the door NOT including the $75 rebate (I.e. $225 + tax). If it breaks beyond repair and/or wears out, go buy another one.