I used one in an old Norinco 1911 I used to have. It actually helped quite a bit. The gun was not a grouper at all as issued. It usually patterned more then it grouped. After the group gripper, nice clusters at 15 yards (more like large single holes) were the norm. I never measured the groups since it was just a shooter more then a target gun, but I was quite pleased with it post group gripper. I had it in there for quite a few years before I sold the gun. The gun did start having some feeding problems just before I sold it (after many thousands of rounds), but I never went into diagnosing the problem before I got rid of it, so I can't say if the gripper had anything to do with it.
I have used them on several guns and found them to be a good addition. THey really shine on older guns that have been shot a lot by making the lug contact the same shot to shot. I have neveer had a feed prob with one that was properly fitted.
I used the Group Gripper also. I also agree with the others above - use a fitted barrel bushing to maximize your accuracy gains. Actually, you may try just the bushing first. That is a key component to accuracy with 1911's.
Used one in one of my Norinco 1911s. It shot fairly well before, but the group gripper helped to eliminate flyers that would spoil the group. It also took the spring out of the barrel hood. No adverse affects with regard to function and condition of the barrel/slide lugs. I'm sure that the link will fail eventually due to extra stress imparted by the notch and spring , but that is an easy fix. Easily puts 5 Rounds into a ragged hole at 15 yds with stock sights, barrel, bushing, and trigger. Holds 3" groups at 25yds off hand, with the only flyers coming from less than perfect manipulation of the trigger on my part. A trigger job would probably tighten it up a notch and a fitted bushing might not hurt, provided I can shoot well enough to notice the improvement.
Buddy is going to use one on a 1991 Colt Commander, so I should have more empirical data soon.
If you're wanting to tighten the group on a loose pistol, the gripper is the best answer for economy. It won't get you to the 50 yard accuracy of a 'smith fit NM barrel and bushing, but if you fit a NM bushing along with the Gripper, I suspect the difference will be a shock. It's that good!!