I built the Heathkit uMatic Keyer in 1983 and found the basic function to be inconsistent and unreliable. The rest of its features e.g. memories, code practice etc are excellent though.
There are two basic failings:
-The idea that an operator can keep his fingers really close, but not touching the paddles for more than a few minutes without direct concentration.
-Unreliable actuation due to variation in humidity, skin dryness, paddle surface and contact oxidation.
I tried wetting my hands, using hand lotion, buffing the paddles and contacts befor each use, applying Brylcream to the paddles, applying contact enhancers to the paddle contacts.
If I was to experiment further I would try making paddles from copper PC board for better resistance and better conductivity.
A neat concept implemented in solid state was innovative for the early 80's, but just proved unreliable. I love all the rest of the features it has.
photo courtesy boomerssupply.net