Terrain safe - just 40 years of helicopter experience, mostly military, and a fair bit in very turbulent conditions in mountains. I have also operated in and around FW - FJ and ME - and never encountered anything more than a burble from wake turbulence - even in and out of LHR..
I've been a controller for over 30 years and after applying the rules never had a problem either. So therefore the rules work well and keep everyone safe.
ShyTorque But these 2 aircraft are in the same wake turbulence category and so require no wake turbulence spacing between them. I don't think that this is done for smaller helicopters (but accept that it's mission dependant rather than size).