KZ themselves seems to have 2 versions. A regular one, and an "ultimate tuning" version for the same price that is newer. If you use aliexpress, you probably won't be told which version you get. Using KZ's Taobao link is the only way to know for sure it seems.
I got mine from aliexpress btw, and this version sounds awesome. I am buying the one directly from KZ just to be sure, because its $6.
Any of the aliexpress sellers should be ok. That's where I got mine from. I am buying the "ultimate tuning" version directly from KZ on Taobao to see if there are any differences.
Any of the sellers on aliexpress under $20 are all fake, despite saying original. I submitted a claim for a counterfeit, just like ebay.
Be sure to report your findings after you receive it.