We've been issuing service pistols with magazine disconnects for over 20 years. While I initially accepted it as the price of getting semis, I've come to appreciate the device.

First, there are all those officers saved by them in gun grabs. This was hashed out on a restricted website for LE firearms instructors. In less than 24 hours we had 30+ saves.

Second, if your weapon goes schlub instead of bang, a tap/rack/ready (otherwise known as an immediate action drill) takes care of the problem. Which, incidentally, is exactly what you'll do if your pistol fires your chambered round, but can't feed the next because your mag dropped. I'll also note that not firing the weapon with a partially seated mag can save you from dropping the mag due to recoil. An IAD is a lot faster than an easter egg hunt for a dropped magazine or a reload.

Third, those folks who harp on being able to fire the chambered round while reloading ignore the times in which you're supposed to execute a tactical reload: from behind cover during a lull in the action. Since you don't remove the partial mag until the fresh one is at the gun, any delay is minimal if an adversary materializes where they're a threat.

The one thing the OP hasn't brought up is where he's going to get the parts to install his magazine disconnect. The factory isn't going to sell them since they're safety items. He'll have to search out someone who removed them from their weapons. Or, buy a sear block with the parts and install them into one with a thumb safety if they'll fit.

One last thing, comparing the trigger action of the M&P to that of the Glock is comparing apples to donkeys. The Glock is the world wide leader in negligent discharges. Something the longer, very slightly heavier, (much like a very well tuned double action revolver) trigger action of the M&P makes less likely.