The improved sear
is the trigger upgrade. The sear shortens the reset. If you are thinking of the physical trigger you put your finger on, that is the same as a non-PC Shield as far as I know, but the way the trigger will behave is modified by the better sear they have in place with the Performance Center models, and the Performance Center M&P M2.0's reset is significantly shorter than that the regular M&P M2.0. It is like night and day comparing the two guns I wrote about earlier. Don't get me wrong, the reset on the standard M&P sear should be acceptable to most, but if someone has other firearms that have significantly shorter resets, it might be advantageous to take advantage of a shorter reset when possible to avoid short stroking the trigger when switching among different pistols (or at least to make things a little more consistent for one's style of shooting if reset is important).
What I can't answer is whether an Apex sear is better than a performance center sear (for all I know they're the same thing). I can tell you that my performance center sear is certainly short enough, but it isn't as short as say the reset on my SIG P229 with its SRT installed, or the reset on my Beretta PX4 Storm Compact now that I've added the new LTT OP Trigger Bar (I would say both are about 1/10th of an inch), but it's still short enough that I can't see short stroking it (at least I can't see myself doing that).
What I also can't tell you is how the takeup and trigger pull has changed because I only have a M&P M2.0 Subcompact and not a non-Performance Center M2.0 Shield to compare my PC Shield M2.0 with. I can tell you, however, that the PC M2.0 Shield has less takeup than the M&P M2.0 Subcompact, but this may also be in part due to the difference in trigger design between regular M&P's and M&P Shields (the latter are literally thicker as shown below, so there appears to be less overtravel). As you can also see in the picture, the polymer overtravel stop built into the frame behind the trigger is also larger on the Shield, so we're never exactly comparing apples to apples when discussing M&P's and M&P Shields. But Apex does claim that their sear does reduce over travel and trigger pull weight in addition to the reset.
Interestingly enough, the parts compatibility is more complex than Smith led on. For example, if you go to Apex's website and look at their fully machine sears for the M&P and M&P M2.0 (both regular and Shield models), "Part# 100-074 is for use in the original M&P series pistols in 9mm, .357SIG, and .40S&W only, and the Shield 2.0 in 9mm and .40S&W." Meanwhile, "Part# 100-063 is for use in the M&P 45, M&P M2.0 models in 9mm and .40S&W, and M&P Shield (9mm/40S&W/45ACP).
In other words, the M&P M1.0 and M&P Shield M2.0 use the same sear but the M&P M2.0 and Shield 1.0 use a different one. Weird, right? (
Fully Machined Sear)