Robert and Charlie, I'll agree with both of you...

I, personally like the stock grip much better on a shotgun.
Unfortunately with the 20" barrel this stick will be hard to maneuver around home, not to mentioned that it's too long even with the pistol grip
I got on it right now... Remingtons are very nice guns, from what I shot, I much prefer the 870 Marine edition than the one Robert have,
but I never shot the M877 Nitro Mag and really have no opinion, even very familiar with the specs. As long as you like it and used to it, this is all it matters.
In general, I find Remingtons to be slightly faster to shoot than Mossbergs. There is a learning curve with the Mossbergs in regard how to reload faster
but I'm not intending to shoot competition style with it so it won't matter to me really. I find both guns to be fine shotguns.
Now, truth be told, the 590A1 are heavy, it would be much easier to swing around with some lighter versions, but this was my first shotgun I purchased
long time ago from Gunbroker and it was the only model available, those days, I think I paid something like $360 or so for it, and since I love military stuff I bought it...
The only "mods" that I made was the heatshield I fitted from a lighter version gun, and I got 2 point sling, simply because I got those on all my long guns, I like unification...
Obwiously, I got, I think made by Streamlight, picatinni rail for 45 degrees flashlight mount with a Lumintop, 400lm, wide spreaded beam, light, on it, I don't like more light at home.
Charlie, the "green Olins" are buffered, military supply ( supposed to be) 9 buckshots that are made by Olin corporation.
Good kick and very tight group from this barrel all the way up to around 20 yards, I didn't shoot it further. Walmart used to sell those 5 for $5.
Thank you both for sharing, I really enjoy such conversations, it always worth hearing another gun guy's opinion

Here is my gun, beat up from being drag in to the truck bed in FL...