Oh yes, it WILL screw up the valve stems, I forgot about that. It can make it hell to get an accurate pressure reading after using it. Whew, with a pressure sensor on board that would be a nightmare.
Here's a pic of 'mushroom' style plug, I can't say I like them all that much, some brands are better than others. I prefer a brand that ALSO uses the vulcanizing cement, some are held in place by air pressure only. Air pressure only types tend to leak, temporary repair only in that sense.
