Belts & Chains.
I seem to recall Rotorway use a triplex chain for the primary drive and that there is a history of drive shaft failure, possibly associated with this.They allegedly leak oil from the chain casing in large quantities. I have also read of alignment problems.
I suppose it depends on how well the kit is put together.
Seems chains may not be such a good idea.
There is an aftermarket 'upgrade' to belt primary reduction.
(Dog tooth belt I think).