I hope your experience with the 1187 Super mag is better than mine.
Mine had the flat black finish and it rusted out of the box. On humid mornings, you could watch the thing rust in front of your eyes in the blind. Since it was a finish issue, Remington said it was due to poor maintenance and would not take care of it. I was appalled since I religiously cleaned this gun after every hunt, simply b/c the finish would rust in this manner. This was really the only issue I had with it in the first year, except that it wouldn't cycle lighter loads, but I somewhat expected that to be the case since its a 3 1/2" gas gun.
Eventually I started having more issues, had to replace the feed latch (tip sheered multiple times), and O-rings. I would suggest carrying a feed latch and O-Rings in your blind bag, as they aren't that difficult to swap out in the field and its annoying having your semi-auto turn into a single shot. Again this was annoying, but seemed fine since they were easy enough and cheap enough to repair myself. I would occasionally take it to a gun smith to have the feed latch crimped back in the gun, but it didn't seem to matter since it always rattled out.
Somewhere in my third season of use, I started having major issues. Every time I shot 3.5" shells out of it, the bolt would hang open and not cycle the next round into the chamber. Apparently I had to take it to a gun smith and he informed me the trigger assembly had gone bad. Apparently, the extra recoil from 3.5" shells had caused the parts in the trigger assembly to loosen up and since remington's action depends on the trigger assembly to be the mechanism to cycle the next round that was the issue. So I replaced that. The straw that broke the camels back was when the linkage, that bridges between the bolt and the recoil spring, broke. This really hacked me off since I was beading down on a green head at the time. At this point, my backup gun had more time in the field during this season than my primary, so I decided to get rid of it. I fixed it up, then went to a local retailer and traded it in for a 30-06.
I would like to think these issues were just mine, but b/c my brother and my cousin, who both had an 1187 3" version, was having similar issues and a few more issues as well, I feel that remington's guns have issues.
If you are looking for a reliable gun that shoot 3.5", I would look at Browning, Beretta, Winchester, or Benelli. The supermag may be chambered for 3.5", but it can't withstand the extra abuse from 3.5" shells. So if it can't withstand the abuse from 3.5" shells and it doesn't shoot 2 3/4" loads worth a damn, then what is the point of the gun other than to look rusty, out of the box, on a gun rack.