If a Robbie is flown inside the limits, then they're as safe as the next helicopter. Mast bumping isn't unique to the Robinson series. I remember seeing a film made by the US Army about Hueys getting mast bumping.
What FR did was to reduce the cost of entry into helicopter ownership which let more people learn to fly. And when the most important attribute when flying *anything* is a professional, cautious attitude then those who don't bring that to the party put themselves at higher risk.
I'd hazard a guess that any higher accident rate for Robbie is also contributed to by their sheer number - you see a lots of crashes involving Fords and Toyotas, less involving Ferraris and Lamborghinis, but they still happen.