History is probably a good predictor of future success in reverse engineering high tech aircraft. Soviet copies of the Concorde, Valkyrie, and space shuttle come to mind.
The TU-144 was a parallel development to the Concorde, and actually flew first. It was also bigger, heavier, less fuel-efficient, and lacked some of Concorde's advanced features. Despite the theft of some plans, there's little evidence that any of it made it to the Soviets or had much to do with the TU-144's final development. Boeing's proposed SST also looked just like the Soviet and UK/French planes - apparently 60s SST design testing all led to the same conclusions. The same can be said of the North American XB-70 and the Soviet Sukhoi T-4, though in the latter case the Soviets were aware of the American plane when designing the T-4. Quite frankly, all five of the big supersonic planes share a lot of design similarities, further proving the point that apparently the "needle strapped to a delta wing" design was the only way to get a big plane past Mach 1, especially with late 50s/early 60s technology. On the other hand, NASA and the Soviets certainly had different ideas about what a space capsule should look like...
The TU-144's problems led to it being withdrawn from passenger service, as it got a negative reputation for safety (two crashes vs. Concorde's one) and was horribly inefficient economically, but the surviving planes (two of them crashed, vs. the one Concorde accident). None of the big supersonic planes were remotely efficient or particularly useful for their intended purposes, in the end, but the four different large supersonic planes that were built all worked.
The Soviet space shuttle, the Buran, worked just fine. The program was cut because of the downfall of the Soviet Union and the resulting lack of funds to play with space programs in the early post-Soviet years, along with the realization (which NASA also came to, through experience), that with current technology, reusable spacecraft didn't give the expected benefits of quick turnaround or lower operating costs. Unfortunately the only one that made it to orbit was destroyed in a museum hanger collapse several years ago.
One could say a lot of quite valid negative things about the Soviet regime. The ability to build functional aircraft was never one of them - their fighters were oftentimes better-performing than their American counterparts, for one example, but the American planes generally had better weapons and avionic systems, somewhat negating the aerodynamic advantages.
Chinese copies of anything are a totally different story. Some are just fine. Others are...not.
