I have an opinion that runs counter to conventional forum wisdom on this topic, but I think is worth a hearing:

I like the trigger on a self-defense gun, particularly one I might carry, to be fairly long and fairly heavy. I do NOT want a light, "like a glass rod snapping," trigger such as is desirable on a range gun.

Why?

I want to avoid accidental (aka negligent) discharges as the pistol is holstered; and I want the act of pressing the trigger, when needed, to require a firm, conscious action by me.

The issue with possibly being sued after a shooting revolves around the idea of a "hair-trigger" gun going off too easily -- say, with a small reflexive movement in the trigger finger -- when the operator doesn't want that to happen. The gun writers talk about situations where people let fly when they really didn't mean to, maybe in response to a loud noise or a movement. If the shooting is not "righteous" that could be grounds for a lawsuit -- if you set the conditions by making your trigger too light. Is that a major problem? Probably not most of the time, but sufficiently so for police forces that they generally ask for heavier triggers (e.g., the "NY trigger") and almost always forbid their officers from tinkering with the trigger on their Glocks or M&Ps. Of note, the Apex trigger -- at around 6 lbs -- is generally approved for use in police owned guns, from what I read on the internet! Ha! I read that on the internet! Well, they do call it the "duty trigger."

Bottom line is that your Shield trigger can be improved by dry-firing it a bunch and/or by polishing up the sear. The M&P factory sears today have a much better geometry to them than the first ones did, back in the day when you had to do your own "Burwell job" on the sear or buy one from some new company called "Apex Tactical."

If your M&P is going to be a competition gun, or a range gun, then there are a number of ways to make the trigger lighter -- including Apex's products. I just don't see the Shield as much of a range gun needing that treatment. As a SD gun, a six lbs trigger is ideal (and readily mastered with some practice).

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S&W Rover