These days with the new rifles, some are welded, some are not. There seems to be no real ryhme or reason.
The original reason these were welded from the get go, was to cooperate with the US regulations so the rifles could be sold in all states. At least that's my understanding.
You only need to replace the chinese unit if it is flawed somehow or is cosmetically undesireable.
Inspect for concentricity to bore with a flash hider alingment tool (most folks don't have this tool)
Check the flash hider base appears level and centered to the flash hider body.
A chinese flash hider that is correcly machined, does not need to be replaced. Also chinese flash hiders are closer to NM internal diameter and this is good.
Muzzle devices that are a direct swap are availlable and you just reuse the chinese barrel's castlenut.
Smith Enterprise - Coast Guard Muzzle break, other smith enterprise muzzle devices(vortex flash hiders) are not legally exportable to canada
Springfield Armoury Inc. - standard usgi type flash hider and they also have a muzzle stabilize/compensator (like a brake) (spcamno lists these in the EE frequently)
Surplus usgi flash hiders - not legally exported from U.S. But pop up in the CGN EE here and there.
About US sourced muzzle devices:
Generally Muzzle Brakes and Compensators are exportable.
Flash hiders are NOT as they fall under the implement of war designation.
There is always a way to get "controlled items" from the U.S. But generally a costly, red tape affair unless these items come already attached to a legally imported firearm.
I'm no expert and the above is how "I" understand the realities of sourcing a "castle nut retained" muzzle device for replacing the factory unit, be it a chinese rifle, a springfield M1A or other version of the rifle.