Buying a used tire to carry as a spare?

I carry an unmounted spare of the same type as my other tires. Altho heavy, I can take it out of the basement compartment or move it around myself. With a rim it may be too heavy for some to handle. Only you know your own weight limitations.
Changing an unmounted tire only takes a few minutes for a tire guy with a pair of tire irons. Just a little longer than it will take for him to install a mounted tire.