Finally got to post answer from VZLÚ (czech aviation research agency and proving lab), where Jetoptera (according to
globenewswire.com did some tests.)
I therefore asked at VZLÚ, if Jetoptera really did approach them and did some tests to find out, if people at Jetoptera mean the bussiness or if it is a complete scam as Nikola Motors was and they simply abused a name of some-small-far-east-country-research-lab.
There is an answer I got from their PR dept. (rough translation from czech language done by me), will provide original on demand :-) :
"Project Jetoptera exists, or, rather existed, because investor experiences financial troubles corresponding to covid-19 pandemy and all development is on a halt for now. Jetopteras choice for our research institute was a logical step, because their demonstrator should use H80 series engine from GE Aviation, and that is offspring of our Walter M601. Moreover, GM facility lies just few blocks around.
To the proposed effecincy of the Jetoptera propulsion system we cannot provide any information, because it is not our know-how and we didn´t participate on its development. Our institute was involved only in testing."
.. so, at least we know they really did some tests (though unable to discern, if they bought the testbed and did tests in-house, or paid for certified testing :-( )