There are direct from Japan ones that are imported, have minor fix-up and are sold. Vietnamese are taken from Japan, to vietnam. There they are apparently run for a few years hard until they need major work. Then they are "rebuilt" from parts from other tractors, cheap labor.
Some here say they are much lower in quality and more likely to break. They are cheaper, apparently.
The tractors start off the same, but take a detour to Vietnam. The people selling them imply they are better because of the rebuild. Some dealerships have apparently found many that have severe problems. The viet tractors come with a warranty--but generally it is parts only, from something they have on the lot (i.e. they take a part off another tractor they have).