While it is a bit disturbing that the root cause of the "mast rocking" (that's what the NTSB calls it) problem has never been found (or Robinson isn't talking if it has), nevertheless Robinson seems to have gotten a usable handle on the issue back in the 2007 time frame, whereby they developed a pre-delivery test for the problem and tuned the transmission mounts to eliminate the issue. Theoretically no ship has left the factory with the problem since, however there is no guarantee that it can't occur later in a ship's lifetime. I haven't read of any problems since 2011 or thereabouts, and all those were pre-2007 builds. As a Robinson owner and pilot I'd be interested in any evidence of this problem in aircraft delivered in 2008 or later.
Meanwhile, it seems much more likely this is a garden variety T&B issue, not some zebra of a mast rocking problem.
As for "mass numbers", a simple check of the NTSB database shows 619 fatal accidents for Bell helicopters (all types) vs. 380 for Robinson helicopters (all types), using a search start date equal to the first NTSB recorded Robinson fatality on 3 May 1980. Leave the ground in any machine at your peril.
I would not be a helicopter pilot were it not for the economics of Robinson helicopters, and I certainly would not be an owner if it were not for the economics of the R44 specifically. To me whatever risk you wish to assign to that is more than worth it.