To me, the electric burner isn't so much the problem as boiling with the flask inside is. You may have gotten away with the electric burner/stovetop so far, but there is always a risk the flask will crack on you and its best that you and the flask are outside when it does. You do not want a half gallon (or more) of boiling wort gushing down your stove and countertop. Nor do you want glass shrapnel scattering in your kitchen. If you are married your wife may be pissed.
I had a 5000ml erlenmeyer crack open from the bottom while boiling on a turkey fryer in the garage. I had used it fine 6 times before but strangely it cracked the only time I tried adding the DME before the water and the DME was not as well dissolved when it started boiling. That was mess enough but I was so glad it happened in the garage where I could hose it out.
Now i am pressure canning my starter wort instead of using erlenmeyers. I was able to borrow a pressure cooker from my mom. I feel that it saves time ( i can make 1 gallon of starter wort at a time for use any time in the future) and is more convenient.