Not stable on mounting shaft [SEP] This is my first electric toothbrush and was given to me by a friend to try out. I bought the new heads after carefully making sure I bought the correct replacement heads. The brush head does not sit down all the way when pressed on and it shakes when turned on. It is not stable and can easily come off.  For me, the spinning brush head is small so it doesn't have room for much toothpaste. Maybe it would fit better on some other model, but it is now not being used.