My two cents worth.
I've never flown a Rotorway, and not even looked up close at one. The tail rotor drive being a series of belts (three in series, any one of which could break) doesn't strike me as an elegant engineering solution.
I've also had some email conversations with someone with very detailed engineering experience of internal combustion engines and gears, who discovered why the Rotorway main drive gear was failing and proposed a solution - I believe this may be the aftermarket solution alluded to earlier in this thread. In a certified helicopter, the failure rate of this critical part would have certainly attracted the interest of at least some part of the airworthiness authorities, followed by appropriate analysis and re-engineering.
But it probably would have been fixed even before it got to production by the requirements for long tie-down testing at various power settings and RPMs. That sort of thing tends to highlight problems pretty quickly - which is why it's done.
After that, the manufacturer does 'function and reliability flying' where the machine is again subject to loads of different tests in flight - all to prove the systems work as advertised (things like cycling every switch in the cockpit every 5 minutes).
It's worthwhile to look at what the highest time any of the homebuilt machines has accumulated without failures - but you probably won't find the data anywhere because there isn't any requirement to keep or submit it anywhere.
And as someone said 'When you buy a certified aircraft, you know you are getting a minimum standard product- maybe not much more than a minimum, but at least it's a minimum. And if the minimum weren't good enough, it wouldn't be the minimum...."
'Nuff said?