Personally, I do not care for mag extensions.
I have this thing about a shotgun being reliable, and being handy.
El Tejon has shared this same thing, and El Tejon has forgotten more about shotguns than I will ever know.
I want a shotgun to be an extension of me, reliable, handy, versatile, nimble, mobile and move and scoot with me - not impede me.
Just me, then again I am old and set in my ways.