The Norinco shotguns have been imported under a variety of brand names, including Norinco, Interstate Arms, Brolin, Hawk, and I think a "New England Arms"??.
They fall into two main types: A very close copy of the Remington 870, and the Ithaca Model 37.
The Norinco copy of the old Winchester Model 1897 is a different issue, more related to Cowboy shooting.
The past imports of the Ithaca 37 copies were POOR quality. They were extremely rough inside, with suspect steels and heat treating.
About the best that could be said of them was that they always went "BOOM" when you pulled the trigger.
At one time, major distributors were selling these Model 37 copies for as little as $80.00, dealer price.
More recent imports seem to have improved in quality.
The Norinco Remington 870 copy is another story.
They certainly are not up to American standards of fit and finish, and are somewhat rough inside.
However, they are all steel, including the trigger guard assembly, and most owners say they make excellent guns, just not up to Remington's quality, even of their "budget" model, the Express.
Most owners are pleased with the guns performance, and say they make good, cheap knock-around, farm, truck, and home defense guns.
At least "some" parts and accessories made for the Remington 870 will fit the Norinco, but NOT barrels.
Magazine extenders are a problem, since the Norinco design places the barrel support ring farther forward on the barrel, to allow the gun to hold one extra round in the magazine.
Most magazine extenders will be either shorter than the barrel, or too long, due to the different barrel system.