Hard rubber is a much better substance with which to construct a clarinet. It does not crack, and it is much more dimentionally stable than is wood, and will therefore be much less a problem of temperature changes.
If one had a nickel for every student that came for a lesson with a wooden barrel absolutely fused to the instrument because they bind after a couple of band rehearsals, one would be a wealthy person.
Some students have been advised to always keep the barrel pulled out in order to avoid this fusion. Honest.
Hard rubber, like wood grows on trees, but the difference in addition to those above , is the abundance of the available material.
It also sounds better, blends with other instruments better, especially string instruments. This has been my professional experience on a daily basis.
Finally, it is less than half the price of any Greenline clarinet, and suffers much less in terms of intonation.