JohnS, I have to agree with you that the myth has been beaten down, but I strongly suspect that there are many in the tractor community who still believe it. Much like the myth that talking on a cell phone while pumping gas can cause an explosion . . . totally false, been dispelled many times, but still believed by many.
That said, spm22 said that parts can be tricky to find, and there is some truth to that if you expect to run down to the local dealer and find them, because in some areas that simply doesn't exist.
The reality is probably pretty close to what I wrote, that is there are lots of places to get parts, just like there are lots of places to buy the tractors. And the tractors, while generally rudimentary in appearance, must work pretty darn well or there wouldn't be so many of them here. So while many may choose to buy something with more advanced features like synchro, shuttle or HST transmission, there is a big market for a basic machine and Jinma seems to fit that market very well.
When things get muddy is when someone is trying to price Jinma "feature for feature" against other brands. Switching from R1 tires to the far more popular R4s can add $1000 to the price of a Jinma. More advanced transmissions are simply not available at any price. But again, the full featured market is not where Jinma is competing. In the basic tractor market, I'd say that Jinma probably owns the category.