TWF

It is not but you can feel when tire is going flat, at least I can. Like I said, personally I have no problem with it however if you are not comfortable riding with plugged tire don't, get new tire.
I had flat tire and delaminating tire on my race bike few times, no big deal.

Slithr

The one piece plug/patch combination works fine. I've ridden thousands of miles on them with no problems, heavy bike, high speed turns, etc. I used them in tubeless tires.

Duke Togo

use it as an excuse to ditch the stock tires - sell them and buy some competent bt-016's ect - the crown on the factory dunlops gives me more issues than tire patches do.

devildust

i had a small piece of metal in my busa, probably rode for 2k miles like that. Drag raced and everything but it was a slow slow leak