Salesman told us go glass top for canning.   Showed us electric coils that had been bent due to the weight of the canner, so I'd like to think he knew what he was talking about.   My mother also had a glass top, had one of the first one piece tops to come out in the early 70's.   She used it for like 25 years before it finally cracked.   She wasn't canning at the time when it failed.    Beats me why canning should be hard on a glass top.