I have an 870P of recent production with the walnut stock and the 2+ factory extension. I also purchased an 870 Express 18" with the factory 2-shot extension and put a laminate stock on it. I think the difference in price was 300 bucks for the two guns, but I also paid for the laminate stock that didn't come with the regular 870 Express 18". I gave the Express away to somebody as a gift. I bought the Police to replace it.
My observations:
They're both 870 shotguns. They both operate the same basic way, and they were both 100% reliable with cheap shells, slugs, buckshot, etc. They both went bang when they were supposed to go bang. In fact, the person I gave the Express to reported that he took it out and was firing it until it was insanely hot and it never skipped a beat. I have heard that newer ones are rougher in the chamber area that may require polishing. My 870 P is a newer production one without the "M" serial number but it has been 100%.
When I upgraded from the Express to the Police, I found the following things:
-The parkerized finish on the Police is significantly better. Miles ahead. The cheap finish on the Express felt extremely rough to touch, and it had a rust spot on the receiver that could never be removed. Horrible finish. On the 870P, I will spray it down with oil and let it dry. It takes the gun from a light grey colour that it comes in and turns it almost black.
The receiver on the 870 Police also seems much more nicely finished BEFORE the external finish went on.
-The springs on the gun feel heavier. Even pushing the loading gate up takes more effort. The mag spring feels heavier. The safety feels heavier. Even when I dry fire it, the firing pin sounds like it hits with more gusto. Some could be legitimate upgrades, others could be because the gun is newer than my Express, which had a bunch more rounds through it. This makes loading shells into the mag tube more of a #####, because your thumb really has to fight that heavy spring. My 20" 590A1 has a significantly weaker mag spring, and the shells go into that tube a lot easier. The Mossberg open-bottom design is a lot more friendly for loading. I was going to say "in my opinion" but I think that's universal, but I'm not here to start a Mossberg vs Remington debate. They're both great shotguns and I own 'em both.
-The recoil pad on the 870P is a Limbsaver. I don't think the recoil pad on the Express was very good in comparison. Didn't even seem like a recoil pad as much as a rubber cap at the end.
-They both come with the same cheap orange plastic follower. For the price of the 870 Police, I wish they used a better follower. But the orange plastic factory one has not been problematic whatsoever.
This is my 870P
This was my old Express:
