I guess you could say I am a "USER"!
I've been using the tire plugs for over 30 years, and never had one fail. I was a homebuilder for 29 years, and construction sites were great places to pick up nails, etc. I had one Michelin tire that had 11 plugs before it wore out, and never a leak. I had a heavy duty trash trailer with 90 psi tires that received a few plugs, and never had a failure.
Is a repair from a tire dealer with a boot the best repair....probably yes. But, a tire dealer is not always handy for the repair. So don't discount the viability of the plug. If you ream out the hole properly and insert a good quality plug, I think you'll have a zero failure rate also.
And installing a plug is much easier than removing the flat and installing the spare.