Mossberg or Remington? Um….. both? I'll be focusing on the 590A1 in this review however. I've had several over the years including the 18.5'' model which is probably my favorite due to the balance of it and the availability of 1 & 2 shot extensions. Here's what I've found over the years with my 590A1s though.
-Extremely reliable. So long as the shooter does his/her part and doesn't short stroke the gun there's an very high probability that the gun will go bang when you want it to. No gun is infallible but this one's about as close as it gets.
-Tons of different factory options out there. Different stocks, sights, finishes, ect…. can be had from the factory.
-The 590s give you the ability to add mag tube extensions.
-The safety location is equally ergonomic for lefties and righties.
-Heavier barrel vs. the 500s.
-The shell lifter stays up when loading it.
-Metal trigger guard.
-Relatively expensive compared to other pump guns.
-Some folks will consider the aluminum receiver to be a con for the gun (I don't think it matters either way as the lockup is still steel on steel).
All in all the 590A1 is as good as any pump shotgun out there and better than many. It's seen military/LEO/competition use for many years and continues to prove itself time and time again. Here's a video with some shooting and a discussion of the pros/cons/features of the shotgun: