Isnt that what is happening when you are riding down the road? the road has small rocks, debris, etc. that are pushing against the tire/plug
I suppose in a perfect world, it might, MIGHT be possible for a rock or any other type of debris, that would be the same EXACT SIZE as the plug, to line up EXACTLY RIGHT with the plug and at whatever speed, 10, 20, 60, 80 mph, TRY and push that plug back in while the tire is rotating at whatever rpms at whatever speed. And it would have what, maybe 1/100th of a second, at whatever pressure, to ATTEMPT to push that plug in.
No, I'm not buying that test, not at all. There were large companies (tire repair shops) trucking companies, and a lot more, that used those mushroom plugs with air guns to install them for years and years and had pretty much zero failures. As stated earlier, Fortnine's a pretty good guy, does pretty good evaluations, does decent reports and is somewhat accurate in his declarations.
With the introduction of Discount Tire, Evans Tire, Big-O Tire, and many more, over the years, the mushroom or
Umbrella style plugs have pretty much fallen by the wayside. Primarily because as ploy to win over business, these companies have vowed to repair flats at no cost. And that means a complete tire and wheel removal, breakdown of the tire, internally patch the tire, re-install and re-balance, all for free.
The rope plugs are the dominating DIY and trail repairs with other forms still available. Of course, if you have a motorcycle with TUBES in the tires, well then you don't have a whole lot of choice other than a total breakdown on the trail (or possibly on the side of a paved road) and do a patch job on the tube. Hense, this is why I took 3 days to completely convert my tube type wheels/tires on my '18 Honda Africa Twin Adventure Sports DCT to TUBLESS rims.
That was done in Oct of last year and I've not lost one single pound of air since I installed two new tires on those converted rims. But, in the event I get a nail or screw, I can easily plug that tire on the trail or the road vs removing the tire/wheel, breaking it all down, finding the hole, repairing it with a patch, then re-installing said tire (that can be one serious pain in the a$$ out on the trail or road) , re-inflating and re-seating the bead(s) (which also can be a pain in the a$$ if your little compressor is on the weak side).
Scott