The safest way to plug a punctured tire is with a combination plug/patch. But this obviously involves removing the tire from the rim and reinstallation on the rim.
Most tire stores use patch/plug these days to fix car tire flats.
Patches are OK if the hole is small and near the center of the tire. I have run into problems trying to use a patch on car tire punctures that were too close to the sidewall. In one case, the constant flexing of the sidewall caused the patch edges to curl up and finally the whole patch came loose, causing tire to leak again.
The only practical way to fix a tire punctured very close to the sidewall is with a plug. Do not attempt to plug a tire punctured on the sidewall itself, except in an emergency and then be very careful, limit your speed, and replace the tire at first opportunity.