all my bikes have always used tubed tires, so no plugs in those.
but i have plugged more cage tires than i can remember (all with the self-vulcanizing plugs...no glue). only ever had one fail...and that "failing" was a very slow leak--had to make sure to put air in it about once a week.
if you are uncomfortable about the plugs, though, you can remove the tire from the rim and patch it from the inside "the right way". they sell those kits in auto parts stores, too. (it's kinda like an innertube patch, but you put it on the inside of the tire instead of the outside of a tube.)