The very best plug is the Mushroom Plug. I don't even know who makes them but they have them available at my local Suzuki Dealer. I have the priviledge of using their tire equipment so I change my own tires there as well as patch/plug them.
The patch looks like a mushroom, a patch with a stem. I simply clean out the puncture hole along with roughing up the rubber on the inside. Apply a light coat of glue on the tire as well as on the base of the stem, let it dry for a couple of minutes then push the stem through from the inside until I can get a grip on the wire tipped stem with pliers and pull it through until the mushroom patch is firmly seated. Use the little metal roller to compress the patch into the glue, snip off the excess stem on the face of the tire and Wal-aaa! Done!
I've run lots of street tires out after picking up a nail or ? and found these patches or plugs, whichever you want to call them, works very well. I have a rule never to exceed tripple digits on a patched tire.
As far as plugging a tire on the road to get you home, I have done that as well but I'd never trust a tire with a plug from the outside. To make a tire safe you must dismount it and repair it from the inside.
Most dealers won't repair a flat. It's easy to understand the liability and why.