The one thing that im a little concerned about with the DL4YHF keyer, is the speed control. Designed to give operating speeds of around 6 to 40 words per minute, ive found that around a third of the track of my 100k control pot has no effect, and the range of speeds likely to be usable to me (the 8 to 25 wpm) are covered by a relatively small rotation of the control.
I found out from a bit of research that the speed control is non-linear. I could try a log pot to see if I can cancel out the non-linearity inherent to the design. But probably a better way would be to determine the resistance either end of the range that is useful to me, and redesign the pot and its series resistor to give me just that range of resistance across a full rotation of the control.