if you bought a full size bike how much will a roof rack or bike carrier cost you ? probably way more than what you will pay for the folding bike
a folding bike will fit or can be used by almost everybody in your family from child to grandpa ..a full size bike will only fit YOU !
there's nothing to think about the folding bike is the best investment you'll ever make for your health and for your personal transportation the WHOLE CLAN or FAMILY can use !!!
if you didn't like it you can sell it for the same price you paid for it probably even more in a couple of years. As gas prices go up people would want to bike more and the folding bike is probably the best solution as you can throw it in the trunk no one would know you have a bike in there.
a full size bike on a roof rack or carrier is an invitation to theft. NOTHING beats a folding bike !!