These plug kit are similar to the ones tyre shops use very easy to do but they don't plug side walls. I used to use them on my road bike R1 they lasted the time of the tyre approx 8000km but that was the tyres life.
I have recently plugged my friends maxxis bighorns and he has done 15000km since then without any leakage or drama. In saying that these shouldn't be used for long term really to get you out of a jam and to the nearest tyre shop and they can use a proper internal patch if the tyre is near new. If it only has about 20000 km left I PERSONALLY wouldn't bother and run with the plug in just move the tyre to the rear wheels.