In the lower areas some folks use swingle and have no problem with it. It is a good rootstock. Its vigorous, produces a tree that is a good size and does not alter fruit composition. There are more rootstocks that are "nearly" as hardy as poncirus....depends os what size tree you want, its import to the fruit composition and where you will grow the tree. Rootstock is a choice that needs to address these factors in a positive manner.