Sooo... here are results of my investigation:

I met Sergei in Berlin at Inside Bitcoins https://www.hashcoins.com/news/inside-bitcoins-berlin-2014/
He was reaally surprised when I asked him to show his ID, but here is the result: http://imgur.com/Giaiooj ,
However after that I decided to check their company in Tallinn and was pleasantly surprised when their CTO personally met me at their offices http://imgur.com/Ocl4wvv,rJJ0rJv,vl5u0Sy,L38g8qn,OVovO2M#0

So, today I finally placed an order and soon I'll be mining my bitcoins ))