Not in LE anymore, but in armed security for a major school district with a liberal weapons (quality 9mm's only) and equipment policy (black nylon and kydex only). I actually use the open topped 1911 mag pouch you have pictured. I prefer open top for the speed and ease of reloading. In the times I have gone hands on I have not had any issues losing mags, not to say that it couldn't happen.
The only issues I've had with the adjustable ones are they lose tension when you remove one of the two mags. But then, if I am removing a mag, things have already gone way downhill and my gun is either dry, malfunctioning, or the fight is over and I am doing a tactical mag change.
There are some 1911 guys in neighboring LE agencies who carry 3-4 mags on the belt, open, turned away from the body. Policy said I couldn't do that. I just keep 2 extra mags in my armor.