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.