Temtop PMD 331/351 particle counters

[dryhero]

Has anybody had experience using a Temtop PMD331/351 particle counter? Look amazing on paper, features, build quality, etc. However, they are 1/4 the cost of gold standard manufacturers like Fluke, TSI, Lighthouse, MetOne, etc.  ($1,200 vs $4K-46K)Likely using lesser quality sensor(s)? Re-calibration might be difficult (Chines manufacturer). I can't find ANY discussion regarding reliability/accuracy. 

Salespersons for the large, above mentioned brands simply say "I've never heard of Temtop". Which may be code for "Temtop is just as good as ours, but at a killer price".

I appreciate any feedback on anything particle counter, PM related.