I added this new sear to both of my M&P's - one I had done an "internet" trigger job on - and one of them I didn't.
After adding this new sear - I *HAD* to do the "internet" trigger job on the other M&P. The new sear smoothed and lighted the pull - which allowed my trigger finger to feel the interface of the trigger bar and the striker block (in S&W and APEX speak - or firing pin safety in Glock speak) and how ROUGH it felt compared to the M&P I had previously worked on.
Now both of them have VERY NICE trigger pull weights, VERY smooth - and a more discernible and SHORTER reset. All pluses in my opinion and corrects the only real minus the M&P series has - which is a substandard trigger pull out of the box.
I noticed that APEX now offers an already modified striker block which is probably the way to go.
Hope this helps,