I've had a bigger and much more powerful lathe that used fibre gears and my current lathe, whilst having steel gears as standard has a set of nylon (delrin to be exact) aftermarket gears for cutting non-standard threads, that work just fine. I think steel is probably better but nylon will work within the limitations of the machine. In any case, if they do fail, aftermarket gears for the mini lathes are easily available in both steel and nylon.
Whether you think you can or think you can't, you're probably right.