Radiotelegraph operators almost universally use electronic keyers descended from the Vibroplex "bug" mechanical oscillator. A modern keyer is a clocked logic circuit controlled with just two switches, called paddles, mounted such that one or the other or both switches can be easily pressed with thumb and fore finger.
Most characters are struck with a single hand motion in which timing is very important. For example, the telegraphers signal CQ (calling anybody (phonetically Seek You)) is sent with two squeezes of the paddles where the second squeeze emphasizes the right hand switch so as to distinguish it from the first, balanced squeeze. Once the technique becomes second nature the feeling is of just squeezing out one letter after another. For this reason radio jargon refers to paddles as a "squeeze key".
It is, I assume, impossible to operate paddles without listening to the tempo of the outbound transmission to maintain perfect timing. I can work the paddles while holding a pencil in the same hand. This keeps my other hand free to tune my radio or sip my coffee.
This is a picture of the paddles I prefer. I find them to be stable, fast and attractive. They have a ball bearing action and easily accessible adjustments of both pressure and travel. While skilled operators can send at 60 words per minute, I am content to work at half that speed.