The only way the Chinese are able to reduce their costs to this sort of level is by using inferior quality material.
The items will be light and easily cracked, they will offer some rust resistance but will not out last a conventional set of extractors made from quality material.
Having said that the price cannot be scoffed at coming in at less than 50% of a quality set but the age old rules still (and always will) apply;
- you get what you pay for. - if it is too good to be true, it probably is.