Being a contractor I've plugged probably a hundred tires over the years from cars and trucks to Forklifts and bobcats. Never had one fail I can remember. My own truck has probably 2-5 in each tire and use it all the time to tow as well as commute.
Patching I believe is better and maybe the proper way to do it but plugging is still safe and doesn't require the tire to be broken down and taken to the shop.