I just got the black/black synthetic waterfoul 535 ATS from SIR (Not the 2 barrel wood/deer combo) and have fired both slugs and shot.
What can I say? It's as accurate as I expect from a scatter (splatter?) gun. Really easy to take apart, it comes with a recoil pad, 3 chokes, cable lock and was cheap as borscht. It's my first pump (I have an auto 5) but from all my research Mossberg knows shotguns. I'm going to try duck hunting this fall which is why I got it.
My only two observations... The safety is really stiff and the pump has slight rotational play but I don't really have anything to say positive or negative about this. I believe that Mossberg makes everything to mil-spec standards so presumably some play is desirable so that it works everytime.
So... I'm very pleased with it. It doesn't look or feel cheap. PM me if you have specific questions.