I've plugged 4 holes with the sticky worms, some including glue, all 4 leaked about 1PSI overnight.
I don't believe plugs are a safety issue but if I were a dealer I'd talk just like they do and refuse to plug anything.
My new philosophy is:
Patch on the inside when I have the inclination to take the tire off.
I rode almost all season last year with 2 plugs. The leak was no big deal because I check air every ride day.
So far, everything that has surprised me has been completely unexpected.