Watch the video on Heli henri's NZ Herald link to understand why mast bumping is much more dangerous in a Robbie than other 2-bladed helos!
The problem comes when you use a Robbie in turbulence (just the sort of thing you get in mountain flying) - it isn't built for it which is why the NZ DoC have stopped using it.
Yes, it is a cheap way to get into helicopter flying but it was built as a commuter machine not a training or commercial one.
You can pretend all you like that it is as safe as any other helicopter but only in certain (smooth) conditions and when flown considerately.
I've had turbulance kick the **** out of me while flying both the 22 and 44 plenty of times and I never came close to mast bumping, or even low-g!
,...but then again I slowed down.
