My must haves on this excellent piece are a bit different.
A good trigger.
A stock that fits.
A light that works all the time and costs less than the shotgun it's on.Hard to find....
That's it.A trained,cool hand with an 1100 thus equipped is very well armed.
Optional stuff would include that extension, hi viz sights, etc.I'd probably get the extension and maybe a Side Saddle.
I see little advantage to a full stock with PG, but little drawback either. If you like one, go for it.I'd save the money, myself, and spend it on ammo.
I'm no auto expert in AS scenarios, but a loading drill for the 1100 might run something like....
When firing and wanting to reload,keep the weapon mounted using just the firing hand. I know it's heavy, do it anyway. Or, tuck the last inch or so of butt under your shoulder into the pit.
Grasp the shell so that the thumb is at the brass end and the fingers cradle the length. Raise the shell to the loading port and hit the button with a finger tip as you use the thumb to shove the shell ALL THE WAY into the magazine.
Like any other worthwhile method, practice is essential.