I bought a Winchester Defender Combo years ago. It came with both barrels, a stock, and a pistol grip. I use it to hunt with mostly, but once I put the 18" barrel, and the pistol grip on it for play time. The pistol grip was almost at 90 degrees angle from the barrel/receiver. Because of this, you had to bring it to shoulder height to shoot it. The pistol grip portion of the regular stock had like 45 degree curve, and it was far easier to shoot from the waist. If you are going to use a pistol grip on a shotgun, it needs to be a plow handle shape, not an inverted "L". As for advantages, I can think of none, even with a good pistol grip. The factory stock can be used used in more positions than the inverted "L" grip, and in as many positions as a plow handle pistol grip, and when its on your shoulder, you can actually hit something with it.