Not all plastic spinners are created the same. I would never use one of those cheap spinners with the plastic back plate and little screws holding the cone but I do use the nylon spinners with the metal plates, even on giant scale planes. I can't count how many cheap plastics I have seen break and shatter sending out shrapnel in all directions.
The OP only wanted to know how to balance a spinner. The how to is usually printed in the instructions when you buy a prop balancer.