I feel that this modification of the M&P can go one of three ways:
1. Easy way: Apex competition spring kit using the original trigger. Change a few springs and you're home free.
2: Medium: Apex Ultimate Striker Block, Competition spring kit, hard sear, leave the factory trigger or pay extra money for a replacement. Your choice, the trigger stroke will be about the same length.
3: Difficult (but worth it): USB, competion spring kit, forward set sear, FSS trigger.
Changing the striker block is probably the most difficult as it requires the removal of the rear sight.
Changing the sear is not too difficult depending on how many safeties on the gun, magazine safeties, etc.
Changing the trigger isn't so difficult, but getting the pin just right to mount the bar can be tricky.
Advanced high speed modifications for tinkerers and competitors:
I beveled the corner off along the first quarter of the sear disconnector to help with the reset at the lower trigger spring weight. I also clipped a coil off the spring in the trigger safety. The spring required more pressure to disengage the safety than to move the trigger. Seemed silly to me. I also recontoured the contour of the sear disconnector, which is a big boy move and not to be attempted without a spare in hand. I got the take up to nearly imperceptible levels. I broke a trigger bar along the learning curve and was the proud parent of a paperweight for a week.