I bought a Sig 320 PRO full size new in May of 2019. I am a firearms instructor for my department and 3 Officers bought Sig 320's. I bought the PRO because honestly I wanted another gun, but justified the purchase by saying some of the Officers I instruct have 320's now.
Personally I prefer the RMR over the DPP and the Sig optics so I contacted L&M Precision. He offers a Sig cut to RMR cut. When he got my slide it was the first PRO slide he had seen and admitted he knew nothing about them. Since the RMR is smaller (from front to back) he did not have to cut my slide, but drilled and tapped new holes so I could use a RMR. I had him install some Ameriglo plain black front and rear suppressor height sights while it was there.
After that I got a Grayguns laser stippled grip module and a Sig grip weight. In this configuration I fired 5200 rounds, mostly American Eagle 147 grain training ammunition. We issue 147 grain HST for patrol and the American Eagle is our training round.
I started having issues with maintaining my zero on the RMR. I first took the RMR off and put it on another pistol confirming it was not the optic. Two weeks ago I sent my slide to C&H Precision. They are making me a custom plate for the RMR with recoil boss's. I can add that review if anyone is interested.