From the Apex sight:

The Apex Duty/Carry Kit for the M&P Shield was designed to provide the Shield pistol owner a smooth, consistent trigger pull that is approximately 2 lbs lighter (based on variations in factory tolerances) with the advantages of shorter over-travel and more detectable trigger reset.
Expected Results
– Reduces trigger pull by approximately 2 lbs.
– Smooth uptake and reset
– Reduces reset length
– Reduces over-travel
In The Package
Fully machined .45 Sear
Ultimate Striker Block Kit
Ultimate Striker Block
Striker Block Spring
Talon Tactical tool
Shield Carry Spring Set
Sear Spring (1/8")
Slave Pin (to assist with trigger return spring installation)
Rated Trigger Return Spring

The kit has made a big difference in the overall trigger feel on my Shield which had a lousy trigger from the factory. I wanted a way to improve the trigger feel without doing a complete trigger change.