Here in my corner of N. America, my local purveyor of magick elixirs supplies a form of MDPV that sounds different from what you folks get over the Atlantic.
The last batch I got from my retailer (early 2009) was very powdery and clumpy. The latest batch (late 2009) was much more crystalline, almost like fine gourmet salt. There are tiny, hard clumps in the package which I have to break up.
The taste of both is different, as well. First batch, more "mushroomy" and pungent. Latest batch? Slight bitterness but almost a bit of a citrus flavour. Strange.
Both were blindingly white -- I've never seen the fabled "tan" product over here.
I am finding that this latest batch has a more cerebral effect, more "up" and feeling good, less yucky cardio effects afterwards. This is a nice surprise. But I still treat PV with respect.
I only offer this info as a general observation about how the Chinese seem to not be very careful in their synthesis.