Well today a few of us researched PET fermenters, Face book groups etc and I can understand what you are saying, user error, low quality spunding valves, even if they were past a use by date. But logically, taking in all the possibilities which can go wrong, why is it that the only ones with problems are the ones coming from China?
We have also looked up those from Australia, they seem to have a range in their arsenal, including PET kegs. They were released in 2017 so they have stood the test of time and the problems don't seem to occur in their range.
The downside is they are not available here.
I have no interest in fermenting under pressure, I would just like to transfer to my kegs so being able to do that straight from the fermenter would be a bonus for me.