This is a little off track in regards to the Cones, but in regards to Bushes, here's the rub on Poly vs Rubber;-

In regards to Poly Cones, sorry, but it is just the wrong material. Poly is nothing in the world like Rubber and doesn't behave like Rubber. While I've not tried or used it for Cones, I would tend to think that where Rubber will sag over time, Poly will collapse over (less) time. With the Rubber Cones, as long as they are not left to go too far, when swapping these out, if left in a cool dark place, they will come back to their original size and shape over about 3 - 6 months, good to go again. Poly wouldn't. There's also a good possibility with Poly that it will fail (collapse) with little or no warning.