At the start of my career, many many years ago, I used to work in the drawing office as a draughts-person. I used to use an electric eraser which was a very heavy metal gun with the cylindrical erasers we would put inside and they used to spin as they erased.....if you left too much out at the front it used to wobble and go crazy! lol
They were useful but we would not use them too much on our drawings, if put too much pressure on the eraser end, it could put a hole in the type of paper we were using for our drawings, we were using a special type of paper designed for drawing office use.
It is the first time I have seen this pen sized ones, they look great, are they only in art stores?