Harquebus

Ditto on the durability of the plastic gears. If I'm not mistaken, most of the gears in Tamiya tanks are also plastic, or more specifically nylon, and they are quite tough. If you look closely, the gearbox construction and the gears themselves are probably the most precision (and foolproof) thing on the HL tanks and that's not saying much however.

The only difference worth mentioning is that the metal gears will be noisier and will require more lube/maintenance. Nylon gears have a self-lubricating quality to them and they generally create less friction than metal ones. People want metal gears for the cool factor I presume.

Haven't heard a thing about gear failure of any kind in the HL, catastrophic or otherwise.

-Harq