the problem with anything like this is usually the same kinda people that skimp on a cheap junk crank also skimp on the kit, bearings, etc. so its always tough to tell if people are having problems due to the parts or due to the fact that they are cheap dummies with hackass builds.
i've been buying these ultra-cheap china vespa cranks now for a couple years and they run just fine. i wouldn't put one in a super high end build but for low performance kit builds they have held up just fine.
one thing i would say is throw away the wrist pin needle bearing and get a good one. i have seen so many cheap china needle bearings fail its not even funny. I buy the malossi one for all my builds.