The Mossberg just feels and looks cheap, no crome/metal lined barrel, the blued looks cheap on it. My 870 is park and makes it look "more solid". Also the Reciver is Alum not Metal like a 870.
I'm not sure what a "crome/metal lined barrel" is, but both 870s and 500s have steel barrels. The finish on 870 Expresses is not the guns strongest point. Aluminum is
metal and there is no practical disadvantage to an aluminum receiver on a 500, except that the gun is lighter.
A 500 has a better control layout than an 870 in the placement of the safety and slide release. A 500 has the shell lifter up when the bolt is closed and an 870 has it down where it gets in the way of reloading.
Mossbergs are a bit rough out of the box, but if you know which end of a gunsmith's stone is which you can make them into a very smooth, very reliable and still inexpensive shotgun for just about any use.