It's amazing what some polishing, sanding or grinding will do for these guns. I did mine & learned a lot about how it works & how to improve said gun.

I would say getting the marks from the manufacturer polished or smoothed out & tightening my slide was the best improvements for these guns. Tightening the slide did a lot for my trigger pull, the slide does not move now when I pull the trigger. It use to move down when pulling the trigger now it does not but I left some SIDE TO SIDE slop in it because I carry it, SD40VE.