I'm the former owner of a S&W 916. I'll tell you why I no longer own it:
Only one action bar. This makes the forearm wiggle (clocking) just holding the weapon. Also makes for iffy cycling.
The barrel is screwed into the receiver, like a bolt-action rifle. Forget about swapping barrels on it, unless you're a gunsmith (or can afford taking it to one for a sub-$100 gun). Also, spare barrels cost more than the gun's worth from Numrich - the only source of barrels I've seen.
Parts are pricey, when they can be found, due to the dwindling amount of parts left available (nothing new is made for these). Also, most parts that you might need (the ones that break most often) are always out-of-stock - so you'll probably never find one.
Barrel has fixed choke. Mine had a "Modified" choke, which I didn't really like. Having it threaded for either inside or outside choke tubes would be MUCH more than it's worth.
Mine had feeding problems galore, with any and all brands/types of ammo I tried. The magazine cutoff (the lever that prevents a double feed from the tubular magazine) often was sticky, and wouldn't allow a fresh shell to the elevator for feeding.
Absolutely NO accessories are available for it. Forget about mag extensions, shellholders, and just about anything else. Want a synthetic stock instead of the warped wood one? In your dreams...
Personally, I'd only own another for use as either a wall-hanger, or to teach a 5 year old gunsmithing upon. You can find MUCH better shotguns out there, especially used ones, for the same money.
I only bought mine (it was my first shotgun) because I knew nothing about it at the time. After a little research (very little, as there's almost nothing on-line about them), and my own experience with it, I traded it in within a month on a Mosin Nagant M44 carbine in excellent condition. I know I got the better end of the deal!
I'd avoid owning one like the plague, even if it was given to me at no cost.