I know I'm a rare breed who has actually had to pull his handgun in self defense when a road altercation ended up back at my home. I had shot thousands of rounds through my M&P9c and knew that trigger like the back of my hand.. and was glad for the extra weight and pull. It gave the other guy a second to think about his actions and he left.. alive. Had I shot him... that trigger mod would be front and center and a lawyer loves ANYTHING he/she can get their hands on to show your irresponsible. Just sayin'.
As long as we are just sayin', "****".
If you and your properly knowledgable and prepared attorney can articulate why you modified your trigger, IF it ever even came up (statistically insignificant), you don't have a problem. The issue first and foremost is always was it a "good", justifiable shoot. If not, your hung. If yes, the trigger isn't going to matter. I know Ayoob has his documented cases, blah blah, but the facts of each case are different. If a modification of any kind can be justified, if it can be shown to improve the function of the gun for you, the owner/shooter, it's not a problem.
If you choose to make critical life saving decisions based on incredible legal improbabilities, that's fine. If your Shield trigger was great out of the box, as many are, and as I thought mine would be based on internet research, great.
But if someone gets one of the really crappy S&W M&P triggers, and there are a bunch of them out there including both of mine, and the owner chooses to install quality aftermarket parts that improve the performance of the gun, it is better to be alive in court after a shooting than to be firing wildly, missing and getting hit with incoming rounds. I'll take an improved trigger over a substandard factory trigger every time. I don't lose one wink of sleep over it.
Sorry Ayoob. Such stories make for good magazine copy and oft-repeated internet advice, but in the real world, I'll make up my own mind based on much larger perspectives and more important priorities.