You beat on the back of a plastic wedge with a big hammer in this cold weather - It is bound to shatter.
In warm weather they will mushroom and peen over.
Like has already been said . . .
I guess the plastic wedge is just for placing in a cut to keep the cut from pinching?
If you are trying to make the tree fall after your done cutting, then put the ole steel splitting wedge in there and beat your heart out?