EMS
IAS has to be safer although I agree its not so comfortable as the jet will hunt the speed adjusting the climb rate etc.
I used to use VS but now use VS in descent only and IAS in climb so if you are 100% monitoring things VS is OK and in some ways preferable especially coaxing a climb at high altitude but then you have to be very disciplined.
I am sure that the pilot of this plane made hundreds of flights with no problems and it only takes one lapse of concentration or distraction for this to happen especially in a single pilot operated aircraft.
Pace