I suspect being Deciduous complements existing hardiness, but it's also beneficial in reducing desiccation due to a reduction in exposed vulnerable tissue during winter. Initially, being trifoliate, deciduous and cold tolerant are likely linked as they're inherited from Poncirus. However, these linkages should gradually be broken in future generations. There are already examples of some of the Poncirus tastes being less prominent in advanced generations. In my experience, acidity tends to linger into F² generations. Pathways have been proposed on this forum to move beyond such acidity.