I have used them. The accuracy improvement was noticable, but not dramatic. I would not recommend them in a gun with fixed sights. The group gripper spring pressure on the barrel link will (in my guns) cause the barrel to lock up higher at the breech end. This causes the POI to drop. Not a problem with adjustable sights, but I was unwilling to use "Kentucky Windage" or change the sights on my fixed sight guns.
If you are a reloader, I expect you could work up a load that would compensate for the lower POI.