The 2nd stage trigger pull on my 9C is better than the single action on my 3913. The 9C first stage vs. 3913 double action isn't even close. Granted my 9C has the Apex hard sear and USB while my 3913 is stock. I wouldn't attempt to break down my 3913 and do a trigger job other than possibly replacing the mainspring. The M&P was pretty straight forward. There is no transition from double action to single action either.
I'm confounded as to why people would purchase a gun and then throw away more of their money giving it the useable trigger it should have come from the factory with in the first place. To each his own I guess.
As to the "double to single transition", this is much ballyhooed on internet gunboards, but is merely a training issue. In my opinion, people don't train much.....if at all. LE included. Much easier to stick them with a striker fired DAO pistol than to teach them anything, like...how to shoot.
I've never experienced any problem with the alleged double to single action transition "issue". Neither have any of the dozens of people I've trained to shoot. YMMV. Regards 18DAI