The little .40s are tough to shoot well without a good grip so the extensions help. Anything that makes the gun bigger will affect concealment ease - so it's a trade off. When I had one it had the pinky extensions on it...
It is easier to use with the larger mag, however, I have been practicing for the past couple months with the smaller magazine for carry reasons. I now feel very comfortable with potato sized target at 20 yards
My XD sub came with a grip extension to use with a full size mag.
"A strong body makes the mind strong. As to the species of exercises, I advise the gun. While this gives moderate exercise to the body, it gives boldness, enterprise and independence to the mind. Games played with the ball, and others of that nature, are too violent for the body and stamp no character on the mind. Let your gun therefore be your constant companion of your walks." Thomas Jefferson