Re: short barrel shotgun
dlc356, I confess! I eat quiche!
The bird's head looks a lot more comfortable.
A dealer friend used to keep a Pachmayr PGed Ithaca around to lend out to those (often cops) inquiring about PGs.
Something about its conformation concentrated recoil. Few purchased after the sample.
My own experience is pretty much limited to a Mossberg a friend bought, installing the PG before ever shooting it with the buttstock (he was a shotgun novice).
We shot a variety of light birdshot loads ant heavy slug and buck loads, back before anybody ever heard of tactical loads.
I had a nagging wrist pain for several months (like most of a year) and didn't figure it out until after it quit hurting.
I found I couldn't keep a grip on the fore end for more than two shots.
My belief is that barring LOTS of training (which will be unlikely for most, due to the unpleasantness of shooting these), putting a PG on a shotgun is the one thing that can be done to reduce its utility as a defensive weapon. Uncoupling the butt from the shoulder or axilla reduces the inherent pointability of the gun; minor changes in either hand's position relative to the other can produce wild changes in aim, rendering misses across living room distances possible.
I certainly don't believe it's impossible to learn to use something like these effectively, but it will require LOTS of training.