Well, my first hand experience is I changed six O-rings, cost me 2$. That's it. So far I have 30 landings and no leak. Can't complain. I know Skymaster still after 15? years in business are pushing out cylinders with an air leakage. And other defects.
Nothing that comes from China so far is perfect. You can be lucky or not so lucky. It seems that many FEJ customers have little experience in sorting out problems that my show up. Then it is good to know that their customer service is very good.