From my experience, the Stop & Go kit works perfectly. 7 flats in the years I have had the kit and not one failure after plugging the tire. I usually explore areas way off the beaten path and am surprised how many nails I manage to locate on remote gravel roads.
Being a old Boy Scout, I believe in being prepared so I also carry the strings and a bottle of tire sealant. Never had to use them though so I give the Stop & Go kit a 100% endorsement.