I have played with the NY-1 modules in my guns with the 5.5 connectors. While its not difficult for a trained shooter to make accurate shots, even under stress, it is hard to adjust to when coming from a 5.5. I have also tried it with the 3.5 and really didn't notice much difference or any real benefit myself. My M&P 45 is probable a pound or so heavier than a Glock 5.5 and I have no issues with it.
The real issue is probably trigger management and the need for increased training time. Police departments, large or small, don't always get the trigger time everyone needs to have on a regular basis, and qualifications and training are usually designed to meet minimum standards while adhering to budget constraints. Also, there are a lot of cops who aren't "gun" people, and trying to get someone to train on their own time, even dry fire therapy, is almost impossible. As a trainer, the only time I ever seem to get a lousy shooter's attention is when they fail to qualify - all those previous qualification courses where they barely shot the minimum score did not make them realize they needed to work harder. Whether you're a cop or a civilian legally carrying a firearm, that gun constitutes a major legal liability for you, criminal or civil, especially if you're not competent with it under any circumstance.