The Chineese Weber knockoff usually fail right out of the box. Research has shown about 50% failure rate out of the box. EMPI is a Weber knock off builder and seller.
As far as your your question, " What happens with the Chinese one when it goes bad?" The carburetor will run rough, lean, or rich, or not at all. Changing the jets will most of the time help with either lean or rich condition. The build quality of the Chinese Weber is poor at best. In most cases you can not tune the Chinesse Weber to run smooth and fuel efficient.
Here are acouple of videos to help Identify and understand the true Webers.
Identifying The true Weber Carb
Pierce Manifolds Understanding your Weber DGV Carbureter