This might sound a bit odd from an instructor that prefers firearm retention training, but lanyards are BAD. Let me explain my personal experience over my 1st combat deployment.
Lanyards were to be attached to the Beretta M9 as well as our belt. Unfortunately, this meant that if the pistol were ever let go of by accident or struggle that it would wind up muzzle first in the dirt with a live round chambered or worse if the lanyard was not adjusted accordingly.
That meant that once it was let go of, you had to bend down and pick it up or "go fishing" using your lanyard to pull it up (not a good idea). To overcome this, our MP's attached the lanyard to the shoulder strap of our IBA and adjusted the length so it would fall just below or right at holster level. All fine and dandy right? Wrong!
While working one of the entry control points I had 2 separate incidents. The first involved the lanyard. A local national tried to get my attention as I was trying to direct a fuel truck on where to go and refused to back up. He wound up grabbing my lanyard to spin me around and talk to me, the result was that local national being put on the ground rather quickly. It took almost 30 minutes for the translator to explain to him what he had done and what could have been the result. I immediately took the lanyard off and ordered the rest of my team to do the same.
The 2nd incident involved another local national that managed to sneak behind me from another truck and bumped into my firearm side quite hard with his hand directly over my holster. This one was put on the ground with a wrist-turn technique and I had the translator tell him that he could have been shot for what he had just done as I had no way to know that he wasn't after my pistol. Had a lanyard been there it would have made my response more difficult as it would have tied his hand and arm up in the lanyard as I turned to respond.
My team was fortunate enough to never have to fire any of our weapons in self-defense on that deployment.
One of the other teams had a lanyard issue in that their gunner was trying to get into the shell of the hummer to get away from an IED detonation and the lanyard wound up hanging up on the turret. Fortunately the lanyard clasp broke under his weight. It could have easily kept him exposed and resulted in an injury or worse.
So my thought is that lanyards are bad, though they serve a purpose when needed...like entry teams and sweep/clear teams. But consider something else. If you're training to use your firearm with both hands and your lanyard is set up for just one hand, how do you transition to the other hand and maintain the ability to use it as an impact weapon should you be left with no other options? Shootings are likely to be up close and personal, fast, low light or no light environment, violent, and will require multiple shots to stop a threat.