CoreArena stands on its own as an amazing mob arena plugin, imo the physics alone are worth the price.
However, my issue with CoreArena is that it’s missing many of the features that MobArena, a FREE plugin has. Due to this, CoreArena can be quite limited in functionality at times and I wouldn’t consider switching to this on an existing server because of this.
Until CoreArena is caught up with what MobArena offers, I simply can’t get this a full 5 stars.