plastic vanes will not work with trad bows (especially selfbows) if you're shooting off your fist or a small rest. feathers will collapse enough to not effect arrow flight, where plastic vanes will not. save the plastic for wheelie bows with shoot through rests and trigger releases.
...furthermore the creatures of the forest will point at you and laugh, young squirrels will call you names, and the reindeer will no longer allow you to play in any reindeer games.
But from a more philosophical point of view, I am wondering why you were looking into plastic vanes with primitive archery gear? I'm not being judgemental, even though my sense of humor runs to the sarcastic side and all. If it feels like I am pointing fingers at you, point right back at me and tell the whole forum about how I just ordered a set of arrows from Tom Braun
and they have plastic nocks! I'm asking because I have no knowledge of archery outside of primitive, I started primitive and have not evolved.