It has been a very long time (around 1970) since I looked into toughened glass insulators. At the time, there were indications that the glass insulators were more susceptible to vandalism in rural areas because of the way the insulators blew apart when hit by rifle fire. They made fun targets for frustrated hunters.
Sediver claimed that the shape of their insulators made them less likely to break when hit and that even if a whole string was broken, the line would not trip out unless there were an overvoltage.
