As usual, it depends on the manufacturer.
Propellers made of nylon and various fibre-reinforced composites have been around for a while. There are many reputable manufacturers who recommend them. Volvo Penta
, for example, sells their Type X prop , made of glass-reinforced nylon, for use with engines as large as the 5.7 L small-block V8. ( http://www.volvopenta.com/SiteCollec...0%28Eng%29.pdf
Any good idea is bound to spurn cheap
knock-offs. There are undoubtedly many easily breakable, short-lived plastic props being peddled all over the Internet
along with the good ones. Unless you know the manufacturer's reputation, it might be hard to tell the difference.