Suspect the answer to yr original question may have something to do with having twice the number of big gearboxes to maintain (plus angle-turners etc, and two major rotor heads instead of one biggie + a tiddler....
Re the BV234 that self-destructed in Shetland, don't think it was anything to do with blade balance, more a gearbox failure, which will not improve your day in any helo...a bit like a main spar failing in your average plank (sorry, stiff-wing), and about as common, thank God
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Ground tested, no fault found