The 391s I looked at a few weeks ago had receivers that were machined to accept scope rings (don't know if the rings are included or extra). A huge plus if you ever want to mount a scope or dot sight. Scoping a shotgun usually involves drilling & tapping the receiver, buying an extra barrel with a cantilever base, or some kind of wiggly saddle mount.... all these options are less than ideal. Keep in mind the 391 has an aluminum receiver so use caution when torquing down the rings.
Overall I was very impressed with the fit, finish, and feel of the 391. For upland hunting my personal preference is still the 20ga Benelli Montrefeltro (because it's lighter and has wood furniture), but if my wife every gets serious about chasing Ringnecks with me I'd be inclined to get her a 20ga 391. -- Kernel