General consensus on he Chinese "clones" of American shotguns is this:
The copy of the Remington 870 is a good utility gun.
Quality is NOT up to American standards of fit or finish, but you can live with it.
These have been imported under a variety of names, including Norinco, various Chinese production plant numbers, Hawk, Brolin, Interstate Arms, and others.
"Some" parts will interchange, but NOT all.
There's a problem with magazine extensions. These 870 copies have 5 shot magazine tube, where the Remington has a 4 shot tube.
In order to accommodate the extra round, the Chinese moved the barrel support ring farther down the barrel.
For this reason, barrels will NOT interchange, and you cannot use Chinese barrels on Remington guns, and you cannot use Remington barrels on Chinese guns.
This also makes trouble when trying to fit a magazine extension.
Due to to to longer magazine tube on the Chinese gun, an American magazine extension will stick out beyond the barrel several inches.
While nothing to brag about, these copies of the 870 make good truck, home defense, farm, and knock-around guns.
The Chinese copy of the Ithaca Model 37 is, or at least was, quite a different story.
The early guns were ROUGH, and poor quality internally. At one point, distributors were selling these for as low as $80.00.
The current versions are reported to be better made, but I haven't seen one so I can't confirm this.
In the copy of the Model 37 there appears to be a problem with any parts interchangeability.
Some people have reported that they had problems fitting genuine Ithaca stocks and hand grips.
Because of the poor quality earlier versions, it might be a risk buying one of these.
In both cases, since no one has put one of these Chinese guns to really hard use and reported in, long term durability, and the quality of Chinese steel and heat treating is always suspect until proven different.
As above, for about the same money you can buy an excellent used Remington 870 and have a better gun than a new Chinese version.