It's hard to say if the improvement is significant enough for you to notice, especially after you consider the wide range of the quality of stock M&P triggers. Even then, we have no way of knowing how perceptive you are of unwanted trigger characteristics.

What I can tell you is...
The polymer or aluminum AEK trigger alone will reduce the overall trigger pull length by 20%.
Most seem to notice a significant difference when comparing the Apex USB to the OEM striker plunger.
The Apex sear further reduces the overall trigger pull length and weight and most notice an improved reset as well.

You could just buy the trigger and add additional Apex parts further down the road. It's definitely cheaper to get the full kit though.