ND's did increase with the use of the striker fired gun, there was a article written on the DC police that showed a clear pattern of increase with Glocks. A covered trigger guard will only stop a trigger pull while the gun is in the holster. It will not stop an article of clothing, or a finger from firing a round when reholstering. Which is how many of these ND's happen.

Yes police officers did have a good number of ND with revolvers, especially using, you guessed it covered trigger guards. But a well made revolver holster does not need a covered trigger. Strap over the hammer, and a tight fit prevent the cylinder from turning. Not so on a semi with no manual safety. If that trigger is pulled it will go boom, whether there is a flipper, or not.

A lot of undercover officers still carry without a holster. A good giveaway that a person is not a criminal is a holster. They are either a CC holder, law abiding citizen, or a cop. Criminals are not going to trust someone wearing a holster unless that have a clear rep as a bad guy. I carried a beat up 1911 condition 2 shoved in the waste band when working undercover. Keep the belt snug and the gun stays put, even running.