Dont use the cheap coats and clark. Use the good one with the pop up top.
I have never had a problem with it.
The cone threads keep breaking on me or leaving loops on the bottom.
I did find the cones work better if I leave the holder horizontal not upright.
Im trying to use them up since I bought a few of them.
Yes the class told me the same thing just to sell their thread.
I have never had a foot break, that sound like a freak accident.