I don't own the Remington, but do have the Marinecote 590.
1. The coating is extremely durable, much more so than Parkerizing(but it is easy to apply Duracoat, and that is probably as durable as Marinecote(nickel)).
2. The internals are coated in Marinecote as well, which is really nice.
3. I suppose that you can tinker with just about any firearm as much as you want, but my 590 is earlier, and I replaced the tang safety button with steel, and the trigger housing with an aluminum version....and feel this is necessary on both. Ghost ring sights are also FAIRLY necessary, but not totally required.
YMMV...they are both good guns, I just prefer Mossberg.
Best Regards,
STeven Garsson