SSMcG,
I know there have been several shoot your sons M&P, and yes, the M&P trigger takes a bit of getting used to. Although the trigger will smooth out a bit, there's a previous point that, IMO, needs looked into... Has any of the people that shot the M&P , shot them before?
Unless you know for sure, it's very likely the LEO's that shot the pistol have never handled the M&P before. Many LEO's simply are not gun enthusiasts.
It may be worth your while to check this out. If they(people whom have shot pistol) are not familiar with the M&P, find someone in your area to give you an accurate assessment of whats going on.
Too, as Don H suggested, shoot it from a rest.
Contrary to what some want to seemingly believe, It's not at all impossible for S&W to turn out an inferior gun. I.E.... Out of spec bbl bushing(just one example) may not be the norm but have happened. Yours may be one with some sort of problem, but I would check things out before throwing in the towel. I'd also bet if there's something wrong with the pistol S&W will make it right.
Please keep us informed of your findings.