Like RVbuilder2002 said, having the ability to use squeezer sets with a custom gun set holder and a bucking bar with a hole to mount sets on the other end is a nice thing. I had to use it a couple of times on my 7A.
It provides a very narrow tool for shooting flush rivets but you do have to hold on to the gun tip because it will want to walk off the rivet head.
It also allows you to make dimples anywhere, like a pop rivet tool also allows, but in my experience the dimples are sharper with the gun and I don't break the nail.
I made my own out of a damaged AN470 gun set and a chunk of steel for the buck. Drilled 3/16 holes in each.
One can buy same from here:
Avery squeezer set holder for gun