Jim WB8SIW has posted this YouTube video on a Vibroplex bug. He states:
The Vibroplex “Bug,” also known as a “semi-automatic” key or “speed key,” has gained a poor reputation amongst some radio amateurs because many who try to use the device have not learned how to properly adjust and manipulate it. When properly adjusted and manipulated, a bug is capable of producing good, clean, well balanced Morse. This video provides a brief set of instructions on how to properly adjust and use a bug.
If you are new to using a Vibroplex bug or an equivalent device, it is strongly recommended that you follow the adjustment steps and practice recommendations outlined in this video. This will aid you as you develop the proper technique needed to be a first-class radiotelegraph or Morse operator.