I went to the range today. I shot 200 rounds of Winchester FMJ 115 grain 9mm luger. I switched between the light and medium springs and the stock captured spring. The medium spring is very similar to the stock spring system in terms of recoil and muzzle flip, yet it felt a little different. The soft spring, however, is very nice and does its job well to reduce felt recoil and muzzle flip. I was able to stay more on target and was able to have faster follow-up shots. I had 0 failures of any kind the whole session. Now, I'm really wishing I had a romeo sight on my p320 to make better use of the reduced recoil/flip >.<
I kinda wish they made the medium spring a little lighter/softer...or included a second light spring. I don't think I want to even try the heavy spring. Since I only shot probably ~70 rounds through either spring, I'd assume there will be some break-in with the springs with another few sessions. The stock spring I used today only had ~90 rounds on it before this.
For now, I've put back in the stock spring and took out my curved advanced Apex trigger in preparation to send the gun in for the 'upgrade'. If I shoot the DPM systems' spring more, I'll post an update if the springs soften up a little or if I have any failures.