Hi
I dont know specific about Megacut 3d, but when i use stl for 3d printing or cnc, i somtimes need to run it tru programs like netfab to correct the mesh - i have also had great succes with the mesh check that comes with FreeCad. So i check the designs from Moi3D - now mostely - in Freecad, before i send it to the 3d printing or cutting program.